Validate config file before using it

[Shinigami92]

Is your feature request related to a problem? Please describe.

The configuration file created by the user must be validated to suppress undesirable behavior

Describe the solution you'd like

Introduce a validation function that analyzes/validates the content of the file and returns only the valid configuration object
All invalid attributes are discarded

Additional context

While working on #489 several problems were found and some TODOs were added

---

HTMLHint/src/cli/htmlhint.ts

Line 402 in 1f1f448

ruleset = JSON.parse(stripJsonComments(config))

• config must be validated and all invalid attributes must be discarded

[Shinigami92]

This could be addressed after #126