PSI tree reference (regular expressions)

[citizenmatt]

Tracking PR for a branch looking at reference for the PSI trees. Picking off the easy ones first, to figure out a system so we can then tackle the bigger trees, such as C#. This is the regular expressions tree, and is based on the work for the XML PSI tree reference.

Likely to be lower priority than other areas that need documenting, especially when there are docs that are not yet up to date with ReSharper 9.

• Generate skeleton reference files based on tree nodes, utils, navigators and element factories
• Add Overview.md to provide a basic introductory article for the AST
• Add Manipulation.md to provide an introductory article to manipulating the AST. Likely to be very similar to the XML one. Does this mean providing a single general page so that Manipulation.md just points to the relevant pages/types?
• Simple doc comments on the tree nodes
• Simple doc comments on the navigators