add support for AMD loading and tests
add README for tests
move tests/ to test-amd/
Fix bugs in implementation global Howler reference, bad links

- the Howl object refers to a global Howler instance, that it expects
  to exist. Went away with AMD support, fixed by adding it in via a
  closure

- Updated AMD implementation to return the reference to the new
  Howler instance instead of creating a new one

- Fixed links to media (mp3/ogg) files
Merge branch 'add-amd-support' of https://github.com/mostlygeek/howler.js into mostlygeek-add-amd-support
Remove the amd-test folder
Fix a few small issues and tweak how AMD support is implemented
Update minified version and bump to v1.0.13