Allow PHPCS and WPCS to pull from different locations

 * Point to expirimental PHPCS and WPCS for rulset subsets
 * Introduce config file for managing Travis before_script environment
 * Remove phpcs.ruleset.xml since we're referencing a core ruleset

See x-team/wp-plugin-dev-lib#30
Fix .travis.yml syntax error
Use .ci-env.sh (nee .travis.before_script.sh) in pre-commit hook
Fetch and use latest install-wp-tests.sh from wp-cli GitHub repo
Use same WP_VERSION in .travis.yml as WP-CLI's template
Update bootstrap to latest version from WP-CLI

See https://github.com/wp-cli/wp-cli/commit/d9111162635742017d1d20e45de93370e2b8575d
Fix typo in PHPCS_IGNORE
Ignore PHP CodeSniffer Warning on WP_Stream_Filter_Input::is_regex
Fix PHPCS issues new from WordPress:core-extra
Add built-in VVV support to pre-commit hook
Add sample .ci-env.sh to readme
Remove extra linebreak
Merge remote-tracking branch 'origin/plugin-dev-lib' into issue-482

Conflicts:
	includes/extensions.php