Introduce .ci-config.sh to override Travis and pre-commit defaults

[westonruter]

There should be a .ci-config.sh (or something) which exports various Bash variables which can be read-in by .travis.yml and bin/pre-commit.These variables can control things like:

• Allow readme syncing to be disabled (Allow readme syncing to be disabled #28)
• Where to fetch PHP_CodeSniffer from (also should grab from GitHub instead of Pear), and which branch or tag to use.
• Where to fetch WordPress Coding Standards from, and which branch/tag/commit to use.
• Path to phpunit.xml
• Path to PHPCS ruleset XML file.
• URL for Travis build button (for generate-markdown-readme), instead of pulling from the git remote

Others?

[JDGrimes]

2 and 3 are fixed by #35. I'm not sure if 4 and 5 are possible yet or not.

[westonruter]

In #127 the config file is .dev-lib called, but it can also be .ci-env.sh