Request: Extract default exceptions

[mahemoff]

This looks like a good inflections library, but it would be good to reduce the footprint by extracting the octopii, mice, and friends into an optional companion module. There are several reasons to propose this:

• Performance - Particularly when the library's loaded on-demand into a web client, it should be minimal.
• Extensibility and the avoidance of bikeshedding concerns - Rails inflections is now frozen [1] because of all the problems pinning down the default rules. It would be cleaner to factor these out to an optional companion module.

1. http://davidcel.is/blog/2012/07/18/the-current-state-of-rails-inflections/