Added a filter flag, to filter through the *Spec files

This allows to filter through the *Spec.js files, without having to modify Gruntfile.js

**filename**
`grunt jasmine --filter=foo` will run spec files that have `foo` in their file name.

**folder**
`grunt jasmine --filter=/foo` will run any *spec file that is located within a folder `foo*`

**wildcard**
`grunt jasmine --filter=/*-bar` will run anything that is located in a folder `*-bar`

**comma separated filters**
`grunt jasmine --filter=foo,bar` will run spec files that have `foo` or `bar` in their file name.

**flags with space**
`grunt jasmine --filter="foo bar"` will run spec files that have `foo bar` in their file name.
`grunt jasmine --filter="/foo bar"` will run spec files within folders that have `foo bar` in their name.

Thoughts? Cheers