Adding support for enum types in query params
Updated MainStringConverter in order to handle enum types in a generic way
This means changing the StringConverter contract from
`Class<T> getConvertedClass()` to `Optional<? extends Function<String, T>> accept(Class clazz)`
Relying on Jackson's ObjectMapper for query parameters deserialization
Instead of manually registering StringConverters.
This provides symetry between query parameters & body parameters deserialization.
Removing useless StringConverter-related stuff
Merge pull request #48 from fcamblor/enum-in-query-params

Symetry between body content & query param value deserializers, thus adding support for enum types in query params