Rust translation. Please review and approve

D translation

please add more test cases, preferably random.
i was able to pass with an incorrect algorithm

some output from my comparisons, where:

levenshtein_greed is my incorrect implementation

Levenshtein_distance is pypi python-Levenshtein ( https://pypi.python.org/pypi/python-Levenshtein/0.12.0 )

Levenshtein_distance('dqw', 'qciwxuwt') -> 7
levenshtein_greed('dqw', 'qciwxuwt') -> 8

Levenshtein_distance('skbnsj', 'ipm') -> 6
levenshtein_greed('skbnsj', 'ipm') -> 5

Levenshtein_distance('jtbd', 'bcx') -> 4
levenshtein_greed('jtbd', 'bcx') -> 3

my incorrect implementation got 5 339 right out of 10 000 and errs both too high and too low