• Cleaned up the types for FS mixin functions
  - Updated FileSystem constructor so typeof FileSystem can be used in mixin extends clauses
  - Added Mixin type
  - Inlined SyncFS, AsyncFS, and ReadonlyFS
• Fixed typo in Async doc comment
• Typedoc no longer shows re-exports
• Moved typedoc config to tsconfig.json
• Updated package description
• Fixed mkdir and mkdirSync not supporting the recursive option. (#75/#77, thanks @yoursunny!)