Prepare for v1.3.0 (excludes `join()`, `include()`)

Backs out the addition of `join()` and `include()` for a stable 1.3.0 release.
The revert commits will be reverted back onto master.
For comparison with 1.2.1, see https://github.com/lox/pheasant/compare/v1.2.1...rc-v1.3.0
/cc @lox