Version 0.6

Mostly a stopping point pending the long-overdue performance increase (which isn't ready yet).
Provides small API foundations for this work.

Some general code tidy up:

• Make types more explicit about what they mean/do
• More documentation

Bug fixed:

• Small memory leak in get_bounds() function of render.c

API Changes:

• Addition of the dummy function suggest_resize(),
  which will be used later for the more efficient implementation.