Init TagsExtension Module, for extending cling to provide interactive hints

AutoloadCallback: Implementing InterpreterCallbacks to attach the module to cling
   The main focus is on overriding LookupObject so that the information about
   lookup failures are obtained from clang.
   The type of the name is not taken into consideration for now.

TagManager: To manage and lookup information from various sorts of tag files.
   Currently a TagManager object is owned by the callback system.
   This may change in future.

Wrapper: As a base class for handling particular types of tagfiles.
   The TagManager maintains a container of Wrappers.

CtagsFileWrapper: Implementing a wrapper for ctags.
   This class is responsible for generating a tagfile from a given path or list of files.
   It also performs lookups in the file generated by it.

And a few simple file system utils to complement llvm::sys::fs and path utilities
Obey coding styles and indentation.