Fix overwriting existing plurals, singulars, and irregulars

[matthewmcgarvey]

Fixes #17

When you call .each on a Hash, there is an implicit ordering of how it goes through the items. Wordsmith was relying on the first match in that to be the most specific. Also, it prioritized existing pluralizations/singularizations over adding new ones.

Wordsmith::Inflector.inflections.plural("person", "people")
Wordsmith::Inflector.inflections.plural("person", "persons")
Wordsmith::Inflector.pluralize("person") # you'd expect "persons" but it was "people"

This change updates the behavior of wordsmith to prioritize later additions for matching words.

[jwoertink]

👍

[stephendolan]

My hero! Cc @btihen in case you'd be willing to test this out for your use case we worked through with our less elegant "salt the earth" approach.

If you wanted to and need help setting that up, I'd be happy to walk through it together!