Option to use --filterpattern

[sveetch]

It seems usage of --filterpattern option from validator is a useful thing with some stuff like Angular to ignore some required HTML attribute like ng-something="".

This should be a multiple value option, that will be automatically joined (validator expect only one regex).

Think about to add this option to the CLI.

[sveetch]

This is related to old issue #6

[sveetch]

Also we may add another new option like --filterpath which could be used to ignore paths from given pattern(s), this should be a multiple value option alike --filterpattern.

'filterpath' will be useful only for site CLI since page CLI paths are manually defined from user.

Finally, these pattern should be a simple string (not regex?) to avoid some path like when a site is written in multiple languages on their own prefix like /fr/foo/ and just need to validate the /en/ pages.