Merge pull request #1555 from felixmulder/topic/docs

Migrate wiki to docs dir

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+---
+layout: default
+title: "Migrating to Dotty"
+---
+
+Migrating to Dotty
+==================
+
+### Minor tweaks ###
+ * `sym.linkedClassOfClass` => `sym.linkedClass`
+ * `definitions` => `ctx.definitions`
+
+### Member Lookup ###
+`tpe.member(name)` and `tpe.decl(name)` now return a `Denotation`, not a
+`Symbol`. If no definition is found they return `NoDenotation` (instead of
+`NoSymbol`).
+
+### Symbol Properties ###
+Most `sym.isProperty` methods don't exist in dotc, test for flags instead. See
+[dotc vs scalac: Trees, Symbols, Types & Denotations]
+
+### Logging, Error Reporting, Failures ###
+
+There are various kinds of logging:
+  * Errors, warnings, etc: `ctx.inform`, `ctx.warning`, `ctx.error`, ...
+  * Log messages displayed under `-Ylog:phase`: `log(msg)` in scalac =>
+    `ctx.log(msg)` in dotc
+  * Debug-Log messages displayed under `-Ydebug -Ylog:<phase>`: `debuglog(msg)`
+    in scalac => `ctx.debuglog(msg)` in dotc
+  * Assertions: `assert(invariant)`
+  * Fatal errors: `abort(msg)` in scalac => `throw new
+    dotty.tools.dotc.FatalError(msg)` in dotc
+
+
+#### During development / debugging ####
+Instead of `Predef.println`, use `dotc.config.Printers.somePrinter.println`
+[Printers.scala]. Printers can be easily added, enabled and disabled
+without changing command line arguments.
+
+```scala
+val default: Printer = new Printer // new Printer => print
+val core:    Printer = noPrinter   // noPrinter   => shut up
+```
+
+[dotc vs scalac: Trees, Symbols, Types & Denotations]: https://github.com/lampepfl/dotty/wiki/dotc-vs-scalac:-Trees,-Symbols,-Types-&-Denotations
+[Printers.scala]: https://github.com/lampepfl/dotty/blob/master/src/dotty/tools/dotc/config/Printers.scala