Inconsistent method naming convention

[Lanre Adelowo]

All methods in the library make use of snake_case except the invalidateAll method (camelcase).

Relevant links -

https://github.com/silk8192/libcache/blob/master/lib/libcache/cache.rb#L83-L85
https://github.com/silk8192/libcache/blob/master/lib/libcache/file_cache.rb#L61-L66

[salahsheikh]

aha its the java conventions creeping in. I'll rename it ASAP.

[Lanre Adelowo]

Nice to hear that

[salahsheikh]

fixed by #2