Update development/test dependancies to Vagrant 1.5
Add a `.ruby-version` file. Default to 2.0.0-p353.

This matches the version Vagrant ships in it's packages.
v1.3.1
Remove Ruby 1.9.3 from Travis test matrix

The core Vagrant code is no longer fully compatible with Ruby 1.9.3.
add `cache_packages` config option, if enabled and cachier present pass `-d` to install.sh as the cache dir
fix wrong config value (returned `Vagrant::Config::V2::DummyConfig` but not nil!)
expose an `install_script` config option for specifying a custom install.sh. The env var still works but has lower precedence
less but more realistic spec examples
naming things is hard...: rename `install_script` to `install_url`
describe newly added config options in README
fix rubocop warnings reported on travis but not locally?!?
Merge branch 'cache-omnibus-download-via-config' of https://github.com/tknerr/vagrant-omnibus into cache-omnibus-download-via-config