Fix plString ssize_t undefined errors.
Merge pull request #357 from dpogue/stringfix

Fix plString ssize_t undefined errors.
Allow passing a clothing file to LoadAvatar and plStringify whatever we encounter on our way
Implement a plLoadClothingMsg as a clone loading trigger
Add functions for writing and reading avatar clothing files

This also introduces a filename member in plClothingOutfit so it
can determine whether to read the clothing information from the file
or the vault.
Add clothing file functions to the Avatar Python API