Add double metaphone code from Andrew Dunstan. Also change metaphone so that

Joe Conway <mail@joeconway.com>

Commit: 13629df5a124fd657bad2c7650efb4799e3d812f
Author: Joe Conway <mail@joeconway.com>
Date: 2004-07-01T03:25:48Z
Releases: 8.0.0
Add double metaphone code from Andrew Dunstan. Also change metaphone so that
an empty input string causes an empty output string to be returned, instead of
throwing an ERROR -- per complaint from Aaron Hillegass, and consistent with
double metaphone. Fix examples in README.soundex pointed out by James Robinson.

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