Passing all tests. Version bump to v0.1.5

Uses 3 row max for Damerau Levenshtein and 2 row max for Levenshtein
algorithms vs the string1.length x string2.length sized arrays
originally used. max distance now treats 0 as 0 and considers 'Nil' to
mean unlimited (and is default). Returns Nil if $max is exceeded instead
of Inf/-1