[w1tcherrr]

Follow-up to #41.

• RemoveDirectory and RenameDirectory now normalize their input and compare names like FindEntry. Before, materials\ or /materials matched nothing, and materials also removed a separate Materials/ folder that FindEntry can't find.
• RenameDirectory normalizes the whole moved path and moves nothing if one is rejected.
• Fixed a KeyNotFoundException in RemoveDirectory/RenameDirectory when type names differ only in case, e.g. TXT and txt.
• GetFullPath returns a.b. for a file named a.b without an extension, so it finds the file again. x.. is accepted like Valve stores it, and ./.. names are rejected.
• Write refuses to write over the package's own chunk files.