Move spec/corelib to spec/opal/corelib
Cleanup rake tasks
Move every spec inside the spec dir

- {→ spec/opal}/rubyspec
- {mri_spec → spec/cli}, spec/{* → opal/*}
- spec/opal/{ospec → mspec/opal}
Enter mspec/opal/rake_task.rb
Add a dir glob helper for mspec rake task
Cleanup gitignore
Rename "corelib" spec dir to "core"
Move gzip and uglify helpers to Opal::Builder::Util
Quotes
Move mspec/opal stuff back to lib and complete cleanup
Don't rely on local static files

I had a local build/specs.js that gave me false positives.