SoftwareSpec tests are now Resource tests
Reimplement SoftwareSpec on top of Resource
Move formula resources to SoftwareSpec
Track initialized specs
Make top-level resources apply to all specs
Make spec-scoped resources override top-level resources
Download strategies take a resource now
Reorganize resource download methods
More useful error message for missing checksums
create: use resource for checksum detection
Allow partial installation of resources
Convert brew-aspell-dictionaries to Ruby and output resources

This makes the script much more readable, and also allows us to download
the language packs into the cache where they can be used when installing
aspell.
aspell: can't access resources directly in class body
scala: use resources
git-flow: use resources
docbook: use resources
git-flow-avh: use resources
shocco: use partial resource installation
mutt: use HEAD resource
android-sdk: use partial resource installation