Change the color of comment nodes from bright yellow to blue.  Bright yellow on
a white background is difficult to read.  Also include a chart showing which
colors are used by which elements in the AST dump.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203050 91177308-0d34-0410-b5e6-96231b3b80d8