[SPARK-18480][DOCS] Fix wrong links for ML guide docs

## What changes were proposed in this pull request?
1, There are two `[Graph.partitionBy]` in `graphx-programming-guide.md`, the first one had no effert.
2, `DataFrame`, `Transformer`, `Pipeline` and `Parameter`  in `ml-pipeline.md` were linked to `ml-guide.html` by mistake.
3, `PythonMLLibAPI` in `mllib-linear-methods.md` was not accessable, because class `PythonMLLibAPI` is private.
4, Other link updates.
## How was this patch tested?
 manual tests

Author: Zheng RuiFeng <ruifengz@foxmail.com>

Closes #15912 from zhengruifeng/md_fix.

3 files changed, 9 insertions, 9 deletions

diff --git a/mllib/src/main/scala/org/apache/spark/ml/feature/LSH.scala b/mllib/src/main/scala/org/apache/spark/ml/feature/LSH.scala
index 333a8c364a..eb117c40ee 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/feature/LSH.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/feature/LSH.scala
@@ -40,7 +40,7 @@ private[ml] trait LSHParams extends HasInputCol with HasOutputCol {
    * @group param
    */
   final val outputDim: IntParam = new IntParam(this, "outputDim", "output dimension, where" +
-    "increasing dimensionality lowers the false negative rate, and decreasing dimensionality" +
+    " increasing dimensionality lowers the false negative rate, and decreasing dimensionality" +
     " improves the running performance", ParamValidators.gt(0))
 
   /** @group getParam */
diff --git a/mllib/src/main/scala/org/apache/spark/ml/tree/impl/GradientBoostedTrees.scala b/mllib/src/main/scala/org/apache/spark/ml/tree/impl/GradientBoostedTrees.scala
index 7bef899a63..ede0a060ee 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/tree/impl/GradientBoostedTrees.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/tree/impl/GradientBoostedTrees.scala
@@ -34,7 +34,7 @@ private[spark] object GradientBoostedTrees extends Logging {
 
   /**
    * Method to train a gradient boosting model
-   * @param input Training dataset: RDD of [[org.apache.spark.mllib.regression.LabeledPoint]].
+   * @param input Training dataset: RDD of [[LabeledPoint]].
    * @param seed Random seed.
    * @return tuple of ensemble models and weights:
    *         (array of decision tree models, array of model weights)
@@ -59,7 +59,7 @@ private[spark] object GradientBoostedTrees extends Logging {
 
   /**
    * Method to validate a gradient boosting model
-   * @param input Training dataset: RDD of [[org.apache.spark.mllib.regression.LabeledPoint]].
+   * @param input Training dataset: RDD of [[LabeledPoint]].
    * @param validationInput Validation dataset.
    *                        This dataset should be different from the training dataset,
    *                        but it should follow the same distribution.
@@ -162,7 +162,7 @@ private[spark] object GradientBoostedTrees extends Logging {
    * Method to calculate error of the base learner for the gradient boosting calculation.
    * Note: This method is not used by the gradient boosting algorithm but is useful for debugging
    * purposes.
-   * @param data Training dataset: RDD of [[org.apache.spark.mllib.regression.LabeledPoint]].
+   * @param data Training dataset: RDD of [[LabeledPoint]].
    * @param trees Boosted Decision Tree models
    * @param treeWeights Learning rates at each boosting iteration.
    * @param loss evaluation metric.
@@ -184,7 +184,7 @@ private[spark] object GradientBoostedTrees extends Logging {
   /**
    * Method to compute error or loss for every iteration of gradient boosting.
    *
-   * @param data RDD of [[org.apache.spark.mllib.regression.LabeledPoint]]
+   * @param data RDD of [[LabeledPoint]]
    * @param trees Boosted Decision Tree models
    * @param treeWeights Learning rates at each boosting iteration.
    * @param loss evaluation metric.
diff --git a/mllib/src/main/scala/org/apache/spark/ml/tree/impl/RandomForest.scala b/mllib/src/main/scala/org/apache/spark/ml/tree/impl/RandomForest.scala
index b504f411d2..8ae5ca3c84 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/tree/impl/RandomForest.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/tree/impl/RandomForest.scala
@@ -82,7 +82,7 @@ private[spark] object RandomForest extends Logging {
   /**
    * Train a random forest.
    *
-   * @param input Training data: RDD of [[org.apache.spark.mllib.regression.LabeledPoint]]
+   * @param input Training data: RDD of [[LabeledPoint]]
    * @return an unweighted set of trees
    */
   def run(
@@ -343,7 +343,7 @@ private[spark] object RandomForest extends Logging {
   /**
    * Given a group of nodes, this finds the best split for each node.
    *
-   * @param input Training data: RDD of [[org.apache.spark.ml.tree.impl.TreePoint]]
+   * @param input Training data: RDD of [[TreePoint]]
    * @param metadata Learning and dataset metadata
    * @param topNodesForGroup For each tree in group, tree index -> root node.
    *                         Used for matching instances with nodes.
@@ -854,10 +854,10 @@ private[spark] object RandomForest extends Logging {
    *       and for multiclass classification with a high-arity feature,
    *       there is one bin per category.
    *
-   * @param input Training data: RDD of [[org.apache.spark.mllib.regression.LabeledPoint]]
+   * @param input Training data: RDD of [[LabeledPoint]]
    * @param metadata Learning and dataset metadata
    * @param seed random seed
-   * @return Splits, an Array of [[org.apache.spark.mllib.tree.model.Split]]
+   * @return Splits, an Array of [[Split]]
    *          of size (numFeatures, numSplits)
    */
   protected[tree] def findSplits(