Rename browser-versions to versions

Cleanup for bug 1066301
Rename browser-version-features to supports

Cleanup for bug 1066301
Rename specification-section to section

Cleanup for bug 1066301
Rename specification-status to maturity

Cleanup for bug 1066301
Add additional support attributes

* prefix-mandatory
* alternate-name
* alternate-name-mandatory
* requires-config
* default-config

Part of bug 1063578, but won't close until implemented.  Done as part of
bug 1066301.
Replace dashes with underscores

Replace in resource and underscore names.  Part of doc cleanup for
bug 1066301.
Change host and add versioned path

* compat.mozilla.org -> browsersupports.org
* / -> /api/v1/

Bug 1059577 picked browsersupports.com/org/net.  Part of doc cleanup for
bug 1066301.