* Make sure the workspace path actually exists before attempting to pack it.
* Make sure the VPK directory tree file was parsed correctly before unpacking store.
* Log debug output for each pack operation to a file.
* Fix bug in s_DirFileRegex regex pattern, which would include a trailing '_' in the context part of the directory tree file name.
* Fix bug in 'GetLevelName()' and 'GetDirNameParts()' causing it to parse the path as well, prune the path before running the regex.
* Renamed 'GetLevelName()' to 'PackedStore_GetDirLevelName()'.
* Renamed 'GetDirNameParts()' to 'PackedStore_GetDirNameParts()'.
* Write a front-end enable file when building client VPK's.
Make the utility methods statics within the implementation so it could be used by other structs/classes of the VPK builder as well, these utility functions weren't useful outside the class. This also allowed for the removal of the singleton which had no purpose whatsoever.
Standalone VPK tool that does everything the VPK tool implemented in the dedicated server does (pack, unpack), but independent from the game's runtime.
