Improve error reporting

[jdkato]

We currently do a decent job of handling errors but most of it is done silently. Some areas that could use better reporting (perhaps with jWalterWeatherman) are:

• configuration: malformed glob patterns, invalid paths, unrecognized rules, rule name collisions
• rules: missing keys, malformed regular expressions, YAML syntax errors
• linting: unsupported file formats, file I/O errors, parsing errors