Enumerator fixes: Kernel#to_enum and Enumerator#each

  * Implement Kernel#to_enum as an alias for #enum_for
  * Enumerator#each now accepts arguments
Triage specs in spec/filters/uncategorized.
Merge pull request #531 from mieko/categorize_specs

Triage uncategorized specs
Bump version and update the CHANGELOG
fixup! Bump version and update the CHANGELOG
Add a rake:dist example that distributes to CDN
Switch to SVG badges for happy 👀 retinas

[skip ci]
Thread additions, Mutex and Queue

Thread.list reports itself as the current thread, and Thread#new
explicitly disallows creation of threads.

Thread now supports the fiber- and thread-local variable storage
interface

Mutex and Queue are implemented, and behave as expected, given the
single-threaded environment.