Add proper support for postgres enum

[yaroot]

Postgres enums are encoded with PgObject in jdbc (and doobie). PgObject is basically just a (type: String, value: String)pair, doobie-postgres has basic support for it. The approach will be different from other modules so I'd like to get some feedback.

Right now I have the very basic implementation, basically you need to feed a type name (in postgres) to DoobiePgEnum.meta and get back a Meta instance for your enum. I'd like to have a more convenient API but seems hard without using lazy val or macros.

[coveralls]

Coverage increased (+0.03%) to 91.348% when pulling 9aabcef on yaroot:doobie-pg into 0e19f28 on lloydmeta:master.

[lloydmeta]

Sorry it took a while for me to get back to you on this: I had to take a look at https://github.com/tpolecat/doobie/blob/f17d00fae2ba7a46d1dcb40b57a937a9a998abba/modules/postgres/src/main/scala/doobie/postgres/Instances.scala#L147-L165 to understand what was going on :)

I think this is a reasonable approach to supporting PG enums; can you add some tests, etc so we can try/hash out the API?

[yaroot]

Unrelated tests are failing..

[yaroot]

@lloydmeta sorry for disappearing, please have a look, basic support is there. Should this be in a separate package?

[lloydmeta]

After giving it some thought, I think rather than this being something included in enumeratum-doobie, which adds support for doobie-core, I think this makes more sense as a separate module, given as how doobie-postgres is its own separate dependency. Thoughts?

[yaroot]

@lloydmeta done

[lloydmeta]

@yaroot sorry I was unclear, what I meant was not for you to create another module in this project, but to publish it yourself. I haven't myself used the doobie-postgres integration extensively enough to be a good steward for this integration.

[yaroot]

alright, that's fine