Creep: Added FileWalker class

It facilitates operations on files that that reference each other using the path relative to the referencing file directory (i.e. the most intuitive path there is).
Also, added BytesFileWalker, LinesFileWalker and StringsFileWalker classes corresponding to File.ReadAll/WriteAll methods (to be found in FileWalker_Basic.cs).
Also, added ExtensionFileWalker class that chooses the file processing function based on its extension.
Also, I had to use try/finally block at some point. Spooky!
Merge branch 'files'
Docs: Updated README

Also, included "Types" library in the list of directories; somehow forgot this one earlier.