Ignore /doc
Remove references to KCODE and pre-1.9 encoding
Restructure tests for readability
Use require_relative for test_helper

This makes it marginally easier to run the tests separately
Added parameter max_distance to Levenshtein

This allows the algorithm to return faster when only a distance
comparision is needed
Fix: Matrix diagonal check for max distance wasn't actually checking diagonal but all cells
Use nil for no max_distance
Update contributor list
Merge branch 'levenshtein_max_distance'

Adds the ability to stop the distance calculation at a specified maximum for
efficiency where the difference is not important beyond a given amount.
Revert Levenshtein maximum distance

It's not immediately apparent whether this kind of short-circuiting is
actually possible. As it's not been part of a release, let's revert it
so that master contains working code.

* Reverts af21890
* Fixes #15 (or at least defers it)