Structured comment parsing, first step.

* Retain comments in the AST
* Serialize/deserialize comments
* Find comments attached to a certain Decl
* Expose raw comment text and SourceRange via libclang


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@158771 91177308-0d34-0410-b5e6-96231b3b80d8
41 files changed