[Add] MDCDamerauLevenshtein 0.1.0

Categories to calculate the edit distance between NSString objects.

```objc
[@"Central Park" mdc_levenshteinDistanceTo:@"Centarl Prak"];         // => 4
[@"Central Park" mdc_damerauLevenshteinDistanceTo:@"Centarl Prak"];  // => 2
```

MDCDamerauLevenshtein includes two algorithms for calculating
the edit distance between NSString objects:

1. Levenshtein distance calculates the number of insertions,
   deletions, and substitions necessary in order to convert one
   string into the other.
2. Damerau-Levenshtein improves upon Levenshtein to include the
   transposition of two adjacent characters. Damerau states that
   some combination of the four operations make up for 80% of all
   human spelling errors.

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The podspec specifies `{ "OTHER_LDFLAGS" => '-all_load' }`, is that still an acceptable way of doing it? The pod crashes and burns without that setting.