Rewriting prefix matching to return keys.

* Removed ol_val_array
* Fixed up ol_prefix_match to return keys
* Updated docs
Iterate backwards through the stack. Helpful commentary.
Merge pull request #128 from infoforcefeed/fix_prefix_matching

Fix prefix matching
Const in more places! SMASH THE STATE.
Refactor, muteable stack.

- Added a muteable stack because rehash modifies the things it pops off
  of the stack
- Refactored unjar to use a generic 'retrieve' method that I can now use
  in cursor land.
Don't get it. Taking a break.
OH LOOk, THE PARENTHESES MATTEr. FUCK C.
Merge pull request #129 from infoforcefeed/cursor_helper_functions

Cursor helper functions
Added olc_jump and test.
More checks, hygiene stuff, addition of the cursor jump test.
Subdirectory for installation target.
Merge branch 'master' into 118_Transaction_Support

Conflicts:
	c_src/oleg.c
	c_src/test.c
	c_src/utils.c
Scoop stuff, ol_unjar_ds remnants