Final Alpha Milestone

A lot of new things are going on in this version, most notably the addition of a level editor, integration of a level-loading API, and a revamped collision detection system.

The level editor is built in Pygame+Tkinter, and exports a format compatible with the new zen::lvl::zLevelLoader API.

Here's a full changelog (from 71e3183):

• Revamped collision detection system: collision state querying, proper
  detection on triangulated polygons, proper bounding boxes in entities.
• Full support for concave polygons.
• Fully-featured level editor with support for import/export, with a
  corresponding engine API to load the files.
• Tons of minor bug fixes.
• A major rendering bug fix that caused crashes and has gone unnoticed
  for some time.
• General improvements in file parsing.
• Full support for MinGW compilation on Windows.
• Ambient lighting shader.
• Stable animation API.
• Documentation improvements and updates.

This release is set out to be the final major release, and I expect that Zenderer will enter beta very very soon.