Major Gff overhaul.

- Replace GffElement with specific types that encapsulate
  packing, unpacking, some type checking.

- Add GffInstance to create a 'view' into another GFF structure.

- Add all the NWN Gff types to pynwn.nwn.types

- Modify formatting to be more inline with PEP8

- Add dynamic creation of object properties and localized string
  getters/setters.
Remove obsolete Locstring class
Update Container to store objects need to be saved.

- Add pre-save function to ERF
Major overhaul

- Restructure directories.
- Add Model parsing (binary and ascii) derived and updated from
  the Neveredit code.
- Add math library.
- Add new BinaryReader class.
- Add PlayerCharacter object.

TODO: There is a lot of testing to be done.  The mdl readers from
neveredit are old and may or may not be totally accurate.