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

Next design steps:

* [ ] review configuration layout
* [ ] review sniff naming convention
* [ ] review unit test design

Next coding steps:

* [ ] migrate more sniffs to use abstract definition
* [ ] add more configuration files
* [ ] extend PHP 5.5 coverage
* [ ] add PHP 5.4 sniff configuration
* [ ] add PHP 5.3 sniff configuration
* [ ] extend unit test coverage
* [ ] adjust unit tests to work on PHP 5.3 and 5.4 environments