Add Feign.Builder

[codefromthecrypt]

For those who do not use dagger, or do not wish to, we could expose a builder which defines all dependencies explicitly that can be provided. This includes logging config, decoders, etc. This could be modeled similarly to retrofit RestAdapter.Builder or jclouds ContextBuilder

ex.

api = Feign.builder()
                .loggingLevel(BASIC)
                .decoder(customType)
                .target(GitHub.class, "http://foo");

Note that this will still use dagger under the scenes, albeit via reflection. When/if someone wants to switch to pure dagger, they could use the module system directly.

cc @benjchristensen

[davidmc24]

I've started work on this. Expect a pull request sometime tonight.