Add WARNING for camelized identifiers

[hisapy]

As a schema writer I want a big WARNING when I write a camelized identifier, i.e.: field :someField in order to avoid possible errors when querying/mutating the schema.

[jparise]

This seems related to #185.

[hisapy]

I believe yes

[benwilson512]

Just to start the discussion, keep in mind that this is a bit hard at the moment because adapters are a runtime phenomena. That is at compile time when the schema is built, we have no idea what convention you're gonna use.

[bruce]

Because regardless of which runtime adapter is being used, the internal representation will stay static (ie, the schema convention can't change), and because snake_case is conventional for Elixir, I think what we can do is tie a "default" adapter to the schema (and have the system-defined default be LanguageConventions), then have a schema's default adapter decide if a schema's definition warrants a warning.

Slated for v1.3's schema definition changes.

[benwilson512]

@bruce do we want to go ahead with making non snake case field identifiers an error or warning?

[benwilson512]

Note that it will likely help with stuff like #298

[bruce]

I think we should just error. :fooBar just seems wrong, and it complicates a ton of things we can figure out implicitly to deal with it.