- moved Context#isSuccess and Context#isFailure down to result
- make all test files singular
Merge branch 'master' of lukas-renggli.ch:/home/renggli/git/PetitParserDart

Conflicts:
	test/all_tests.dart
	test/core_test.dart
	test/core_tests.dart
	test/petitparser_tests.dart
- added specific exceptions to CompositeParser
- fixed composite parser tests