Add new phonetic similarity: Double Metaphone

[vickumar1981]

Add implementation and tests for double metaphone: https://en.wikipedia.org/wiki/Metaphone#Double_Metaphone

[vickumar1981]

working version from apache commons (written in Java, will need to be converted to Scala):

https://android.googlesource.com/platform/external/apache-http/+/refs/heads/lollipop-mr1-wfc-release/src/org/apache/commons/codec/language/DoubleMetaphone.java