Added support for ignoring file patterns

[nelak]

No description provided.

[jarradseers]

Cool - please can you update the README with this before I merge it in? thanks.

[Bonfims]

how to use?

[rafaelassumpcao]

hey, @jarradseers are consign still accepting PRs?

this one would be very helpful... since it is pretty common to ignore files containing *.test.js for example.

anyway, I come with an alternative solution, ... but changing ignore flag for preserveBasename or something like that and just tests the regex against the basename instead of the extension only.
because with it, we keep the compatibility and open to do things like

consign({
  cwd: 'app', 
  extensions:['^(?!.*test\.js).*\.js$'], // regex  ignores *.test.js but will pass *.js files 
  preserveBasename: true // this is duo to path.extname(location) would be replaced by path.basename
})  

please let me know if we can invest time in it.

Thanks!