0019ca9141
Changes `librustc_X` to `rustc_X`, only in documentation comments. Plain code comments are left unchanged. Also fix incorrect file paths.
The rustc_ast crate contains those things concerned purely with syntax
– that is, the AST ("abstract syntax tree"), parser, pretty-printer,
lexer, macro expander, and utilities for traversing ASTs.
For more information about how these things work in rustc, see the rustc dev guide: