Multi-property sorting + number-safe sorting.
Updated documentation.
Don't attempt array sort when no sort fields present.
Removed references to old "direction" option.
Added test for "sort_empty" option.
Bumped version number.
Test coverage reporting + improved Makefile.
Updated readme.
Merge commit 'cb9d09b3f439bb11175acb6729207696efbf01cd'
Released 0.2.0.