Adds support for HTAB as well as SP as whitespace separators in content-type headers

[rg2011]

Fixes issue #52. Notes:

• The fix applies to both typeis and typeis.is, instead of just typeis.

  This is because typeis.is can receive a req-like or res-like object (this behaviour is undocumented but tested). I wanted to avoid situations where typeis(req, ...) would work but typeis.is(req, ...) would not.

• The fix breaks backward compatibility in that, previously, typeis would fail if the content-type parameters were not properly formatted. But, after this PR, it will just ignore them.

  i.e. previously, this would return false:

  typeis.is('application/json; charset:utf-8', 'json') // Notice the ":" instead of "=" in charset

  But after this PR, it will return "json".

  This behaviour was documented (...If the Content-Type header is invalid...):

  type-is/README.md

  Lines 35 to 38 in 7d19b7a

  	Checks if the `request` is one of the `types`. If the request has no body,
  	even if there is a `Content-Type` header, then `null` is returned. If the
  	`Content-Type` header is invalid or does not matches any of the `types`, then
  	`false` is returned. Otherwise, a string of the type that matched is returned.

  But it was not tested in the case of invalid parameters. I am not sure of the best way forward:

  • Keep validating parameters, and make test cases for it,
  • Or update the documentation to clarify that parameters will not be validated.

• After this PR, media-typer dependency could be upgraded to 1.1.0.