Merge upstream enum property

Hi,

It's me again.

I created an annotation that creates enum types and String to enum value converting methods.

This could be quite handy when converting String types (e.g. from some JSON payload) to enum values.

My original plan was to bolt on methods to types generated with @JsonProperty but I changed my mind since those same methods can be imported as static extensions (mixin methods).

I just realized that this can be used beyond android projects. Ha. Cool.

Please review and merge.

Thanks!