Add info about ParseSess for code index #50

Author: vishalsodani

src/code-index.md

@@ -7,3 +7,4 @@ compiler.
 Item            |  Kind    | Short description           | Chapter            | Declaration
 ----------------|----------|-----------------------------|--------------------|-------------------
 `TyCtxt<'cx, 'tcx, 'tcx>` | type | The "typing context". This is the central data structure in the compiler. It is the context that you use to perform all manner of queries. | [The `ty` modules](ty.html) | [src/librustc/ty/context.rs](https://github.com/rust-lang/rust/blob/master/src/librustc/ty/context.rs)
+`ParseSess` | struct | This struct contains information about a parsing session | [The parser](the-parser.html) | [src/libsyntax/parse/mod.rs](https://github.com/rust-lang/rust/blob/master/src/libsyntax/parse/mod.rs)