Inline now useless Schema::Builder#base_relation
Highlight that we're relying on mutation here
Prefer instance_exec over module_eval plus lvar
Finish builder initialization in #initialize

I like my objects to be ready once #initialize’d. For builder objects,
this means that all state needed to do the actual work of building an
object, is ready.
Nuke last remaining Adamantium::Flat inclusion
Use h as hash memo in #reduce & #each_with_object

Just something I’ve been doing lately and like …
Better localize schema definition builder code
Move definition builder context to its own file
Simplify schema definition building
Nuke unused & outdated Schema::Definition.context
Compute Schema::Definition#fk_mapping in #initialize
Close #16 Support a user defined schema base class
Move instance independent code to a class method
Nuke tempting but unused FKConstraint::Set#[]
Pass strings to Inflecto.singularize

Although it seems to work with symbols, at least on 2.1.2, I have no
idea why, and the yard docs say all methods expect strings.