More tests and other odds and end

 - Add tests that work to pos/neg, tests that don't work yet to pending/pos/neg.
 - Also, change .gitignore to allow for a local directory.
 - Also add a draft page to the docs.

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diff --git a/docs/dotc-internals/core-data-structures.md b/docs/dotc-internals/core-data-structures.md
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+(The following is work in progress)
+
+## Symbols and SymDenotations
+
+ - why symbols are not enough: their contents change all the time
+ - they change themselvesSo a `Symbol
+
+ - reference: string + sig
+
+
+Dotc is different from most other compilers in that it is centered around the idea of
+maintaining views of various artifacts associated with code. These views are indexed
+by tne
+
+A symbol refers to a definition in a source program. Traditionally,
+ compilers store context-dependent data in a _symbol table_. The
+ symbol then is the central reference to address context-dependent
+ data. But for `dotc`'s requirements it turns out that symbols are
+ both too little and too much for this task.
+
+Too little: The attributes of a symbol depend on the phase. Examples:
+Types are gradually simplified by several phases. Owners are changed
+in phases `LambdaLift` (when methods are lifted out to an enclosing
+class) and Flatten (when all classes are moved to top level). Names
+are changed when private members need to be accessed from outside
+their class (for instance from a nested class or a class implementing
+a trait). So a functional compiler, a `Symbol` by itself met mean
+much. Instead we are more interested in the attributes of a symbol at
+a given phase.
+
+`dotc` has a concept for "attributes of a symbol at
+
+Too much: If a symbol is used to refer to a definition in another
+compilation unit, we get problems for incremental recompilation. The
+unit containing the symbol might be changed and recompiled, which
+might mean that the definition referred to by the symbol is deleted or
+changed. This leads to the problem of stale symbols that refer to
+definitions that no longer exist in this form. `scalac` tried to
+address this problem by _rebinding_ symbols appearing in certain cross
+module references, but it turned out to be too difficult to do this
+reliably for all kinds of references. `dotc` attacks the problem at
+the root instead. The fundamental problem is that symbols are too
+specific to serve as a cross-module reference in a system with
+incremental compilation. They refer to a particular definition, but
+that definition may not persist unchanged after an edit.
+
+`dotc` uses instead a different approach: A cross module reference is
+always type, either a `TermRef` or ` TypeRef`. A reference type contains
+a prefix type and a name. The definition the type refers to is established
+dynamically based on these fields.
+
+
+a system where sources can be recompiled at any instance,
+
+ the concept of a `Denotation`.
+
+ Since definitions are transformed by phases,
+
+
+The [Dotty project](https://github.com/lampepfl/dotty)
+is a platform to develop new technology for Scala
+tooling and to try out concepts of future Scala language versions.
+Its compiler is a new design intended to reflect the
+lessons we learned from work with the Scala compiler. A clean redesign
+today will let us iterate faster with new ideas in the future.
+
+Today we reached an important milestone: The Dotty compiler can
+compile itself, and the compiled compiler can act as a drop-in for the
+original one. This is what one calls a *bootstrap*.
+
+## Why is this important?
+
+The main reason is that this gives us a some validation of the
+*trustworthiness* of the compiler itself. Compilers are complex beasts,
+and many things can go wrong. By far the worst things that can go
+wrong are bugs where incorrect code is produced. It's not fun debugging code that looks perfectly
+fine, yet gets translated to something subtly wrong by the compiler.
+
+Having the compiler compile itself is a good test to demonstrate that
+the generated code has reached a certain level of quality. Not only is
+a compiler a large program (44k lines in the case of dotty), it is
+also one that exercises a large part of the language in quite
+intricate ways. Moreover, bugs in the code of a compiler don't tend to
+go unnoticed, precisely because every part of a compiler feeds into
+other parts and all together are necessary to produce a correct
+translation.
+
+## Are We Done Yet?
+
+Far from it! The compiler is still very rough. A lot more work is
+needed to
+
+ - make it more robust, in particular when analyzing incorrect programs,
+ - improve error messages and warnings,
+ - improve the efficiency of some of the generated code,
+ - embed it in external tools such as sbt, REPL, IDEs,
+ - remove restrictions on what Scala code can be compiled,
+ - help in migrating Scala code that will have to be changed.
+
+## What Are the Next Steps?
+
+Over the coming weeks and months, we plan to work on the following topics:
+
+ - Make snapshot releases.
+ - Get the Scala standard library to compile.
+ - Work on SBT integration of the compiler.
+ - Work on IDE support.
+ - Investigate the best way to obtaining a REPL.
+ - Work on the build infrastructure.
+
+If you want to get your hands dirty with any of this, now is a good moment to get involved!
+To get started: <https://github.com/lampepfl/dotty>.
+