Cleanup and refactoring

Please review the code carefully

Changes;
- removed duplicate code, by replacing busted functions with their penlight counterparts
- reduced bootstrapper to only commandline options, moved other stuff into busted
- changed error reporting (test process errors) to be reported as failed tests
- added a set of tests for the command-line options
- fixed https://github.com/Olivine-Labs/busted/issues/88
- added LuaCov settings file

busted can now be used without the bootstrapper, and testfiles are loaded from within busted. This is an initial step towards using lanes. In a new lane busted can be loaded, with same settings and only a subset of test files.

the added commandline option tests produce a lot of output (because of intentioanl errors) so it is best to run busted own test suite with the `--defer-print` option.

It probably needs some more cleanup and refactoring, so please comment.