Add and refactor ZFTool\Diagnostics checks.
Add missing setLabel() to AbstractCheck
Add tests for explicitly-set labels.
Add ChecksTest (100% coverage), fix Check\Callback.
Update README.md on built-in Checks.
Fix getLabel() unit test.
Make Check\ClassExists report on all missing classes.
Fix incorrect array_pop.
Add DirReadable now reporting on all failing directories.
Add DirWritable now reporting on all failing directories.

- more detailed DirReadable and DirWritable tests
- 100% test coverage
- test comments fixes
Fix CS.
Add documentation for Check\Callback.
Add CpuPerformance bcmath check, composer suggest.
Fix CS, imports.
Remove @package
Merge remote-tracking branch 'origin/master' into feature/zftool-checks

Conflicts:
	composer.json
Cleanup.

- Fix imports.
- Fix CS.
- Fix docblocks.
- Add argument validation for CpuPerformance::__construct()
Fix CS.
Add missing docblocks.
Merge remote-tracking branch 'origin/master' into feature/zftool-checks

Conflicts:
	README.md
	src/ZendDiagnostics/Check/AbstractCheck.php
	tests/ZendDiagnosticsTest/BasicClassesTest.php