Add C# support to unite-outline using ctags.

- In the code, refer to C# as "cs" consistent with the vim-filetype.

- Because of the # character in C#, quote the arguments to ctags where
  the # character appears -in forcing the language and setting kinds.

- Add the lang_info.cs entry so that ctags is used for cs.

- Copied the outline_info struct from C++.