support user specified rsync excludes.

This commit allows to specify subfolders that should be excluded from syncing via synced_folder options:
e.g.:
config.vm.synced_folder '.', '/vagrant', :rsync_excludes => ['chef/tmp', 'tmp']
Release Elastic IP before destroying
Fix Vagrant 1.4 compatibility and support multiple SSH keys

Vagrant 1.4.0 added support for multiple SSH keys (mitchellh/vagrant#907)
and changed `private_key_path` to an Array.

This commit ensures we always handle it as array to keep compatible with
both old and new Vagrant versions. Also pass all of the specified keys
to rsync/ssh command.

Fixes #171
Add ProvisionerCleanup to the destroy action middleware stack

Call cleanup method of the provisioners (Vagrant >= 1.3.0).

Fixes #170
Fix #174
Merge pull request #164 from ctso/master

Elastic IP is not released when instance is destroyed
Merge pull request #172 from tmatilai/multiple-ssh-keys

Fix Vagrant 1.4 compatibility and support multiple SSH keys
Merge pull request #173 from tmatilai/provisioner-cleanup

Add ProvisionerCleanup to the destroy action middleware stack
Merge pull request #175 from maljub01/user_switching

Fix #174
use latest vagrant
Merge branch 'rsync_excludes' of github.com:databus23/vagrant-aws into databus23-rsync_excludes

Conflicts:
	lib/vagrant-aws/action/sync_folders.rb
bump fog.io to 1.18.0
release 0.4.1
set version back to dev
fix security_groups override test
add --delete flag

This makes more sense, and better matches behavior of "real" shared directories behave (say in virtualbox).
update copyright year
Showing how to increase disk size
improved error message for missing ami now includes region info
Merge pull request #204 from zelig/master

improved error message for missing ami now includes region info