Merge pull request #8 from tarjei/master

Fix issue where the install fails if one of the packages are missing sources/main.
Updated dependencies, adjusted minimum stability. Added lock file for
composer
Prefering source for installing composer dependencies in travis.
Calling init is no longer necessary, the bower configuration file is now
created during bower calls and will be deleted after the command has
finished. Added cache warmer event which fixes #6. Added new option
"install_on_warmup" to the configuration.
Updated readme to cover installation of dependencies during cache
warmup.
Package names from bower are now correctly converted to valid asset names,
this fixes #10.
Updated readme to cover naming convertion from bower names to asset
names.
Updated changelog