Split into processor & core

[mannodermaus]

This library includes a dependency on javawriter for its compile-time code generation. Since there is only one artifact to include for both the processor and core, this dependency is shipped in the final package as well. Please consider splitting up the library into two separate modules, to have inclusion work akin to other code generation libraries, like so:

compile "com.github.Workday:postman:<version>"
apt "com.github.Workday:postman-processor:<version>"

Only the processor module would then require the dependency on javawriter.

[ndtaylor]

Shouldn't be too hard. All of the code generation stuff has already been partitioned into a separate package (codegen), so all we have to do is put that in a separate module (and move Names.java, which is in codegen and shouldn't be).

[mannodermaus]

Awesome! I can create a PR later this week, if you like.

[ndtaylor]

Works for me. Pull requests are always welcome.

[mannodermaus]

Here is the PR. I haven't touched the README yet to extend the *How to Use Postman" section with the new artifact configuration, though.