Ensured `vagrant user parameters` prints string for keys and not symbols
Fixed merging process in presence of nil keys
 * Nil values are considered as being missing by the merging process.
 * A key with a nil value gets overriden by any value and cannot override
   any.
 * Fixes issue #12.
Merge branch 'fix-merge-nil-values' into 1.x
Minor formatting fixes to CHANGELOG.md
Added an Helper class for dealing with env
Added possibility to export (and unset) environment variables from parameters
 * Bumper to 1.3.0.dev1 , new feature.
Now relying on shellwords module to escape shell variable value
Added env command for Vagrant v1 plugins
Fixed tests on Ruby 1.8.7
 * Wrong syntax used to create a hash (empty: instead of :empty =>).
Merge branch 'feature-env-export' into 1.x
Now using minitest as the test library
Updated CHANGELOG
Small typo fixed in README.md
Improved README
 * Add paragraph about paths expansion.
 * Rephrased a bit how vagrant user env description is built.
Added note about issue-13 in CHANGELOG.md
Released version 1.3.0
Merge branch '1.x'

Conflicts:
	README.md
	lib/nugrant/bag.rb
	lib/nugrant/helper/bag.rb
	lib/nugrant/version.rb
	nugrant.gemspec
	test/lib/nugrant/test_config.rb
	test/lib/nugrant/test_parameters.rb