Fixes bug with freeing transition with no sums listed
WIP - first pass at adding scheme scripting. Functional but slow.

Also, use of scheme vs. a rule file is hardcoded at the moment.
Needs a way to define scheme file to load in data file, or rule file to
load.
Might need to pass the full board to scheme, or register neighbor
counting as a native function for speed.
Might also need to use some forms of cacheing
Makes scheme interface use primitive functions to get/set/count cells
Makes generate() in backend.c call scm_generate correctly
Improves Scheme interface and simplifies the most common pattern
Moves scm helpers to core.scm. Adds board_set_cell() to board.c/h
Put loading of scheme module into rule.c
Added scheme filename/module/function definition to rules file
Removed unused core.scm Scheme module
Made Makefile use glfw3's pkg-config for libs/cflags
Merge branch 'develop' into feature/scheme

Conflicts:
	src/Makefile
Made rule files w/ scheme not need neighbor type or transition data.

Made a run_scm_life.sh for running an automata that uses scheme. Made
run_life use the C-based life rules
Made world global use a _g suffix
Merge pull request #16 from calebsmith/feature/scheme

Adds support for automata rules in Scheme
Added recent changes to change log
Fixes hardcoding of Scheme filename/module/function to use rule file
Documentation improvements. Added docs for rule and Scheme files
Adds links to reference other docs. Moves Scheme API into its own doc
Small tweaks to docs to fix formatting and a wrong link to scheme API
Updates README screenshot of GOL to use a gif