Version 0.4.0

• Bundled commands mention they're included with WP-CLI [#110].
• README installing instructions default to Git installation [#111].
• Improvements to scaffolded CONTRIBUTING guidelines [#128, #124, #117, #131].
• Adds support policy to scaffolded README [#130].
• Converts '~/' when supplied in $package_dir [#127].
• Permits running PHPUnit tests, if they exist [#126].
• Clarifies help text and error messages for invalid <dir> values [#114].
• Fixes error message: expected key is 'extra', not 'extras' [#122].