Add management of hostsfile on the host machine.
Update to do an update of hosts files while leaving existing host structure in place, rather than generating a local hosts entry automatically.
Merge branch 'master' into new-hosts-os-hosts-file

Conflicts:
	lib/vagrant-hostmanager/config.rb
	lib/vagrant-hostmanager/hosts_file.rb
	locales/en.yml
Fix overwrite bug that was inadvertently regressed in the merge.
- Ensure that empty regex isn't processed for deletes.
- Set the hook for deletion to run prior to machine deletion so that the id is retrieveable.
Cleanup tempfiles when done.
Add support for managing host /etc/hosts file.

This commit also include preservation original /etc/hosts file on
guest machines.
Clean up plugin configuration and add comments.

This commit cleaned up the plugin's configuration and added code
comments for the hosts_file module. Additionally, display messages were
re-organized based on the single action.

The command still requires code to validate the configuration before
execution.

This closes pull request #18. Thanks to @b2jrock for his contribution.