Currently rustbuild isn't detecting the `-O` flag for tests via the
`--disable-optimize-tests` or not command line flag to `./configure`, and this
commit patches up the support to pass `-O` by default.
This commit expands the bootstrap build system's `README.md` as well as ensuring
that all API documentation is present and up-to-date. Additionally a new
`config.toml.example` file is checked in with commented out versions of all
possible configuration values.