experimental bootstrap and multi-version compat feature

Adding new features and coverage at the same time:

* bootstrapping and composer autoloading (with fallback where composer is not available)
* support for `--runtime-set` to specify PHP version ranges to test for
* PHP version range can validate minor version differences
* add abstract sniff
* add sniff configuration from file (@reneoelke hopefully this is somewhat acceptable?)
* allow to print verbose PHP version a configurated sniff failed for
* add deprecated function names configuration from PHP 5.3 and 5.4 for demonstration