Better modularization

[holograph]

Currently accord-core contains both the matcher library (required at runtime) and the definition DSL (strictly not required at runtime). Better modularization, to e.g. accord-matchers and accord-dsl (with accord-core aggregating both for backwards-compatibility) is desirable, and might enable full elision of infrastructure code in runtime dependencies (e.g. TransformedValidator, which is really only required at compile-time).