Added support for the logical operator `or` for media queries. Closes #2

Also moved `media type` from the `mixin` to `function` to be able to chain it along the comma-separated list of queries.

By default,
- Under the `mixin`s, the `$type` is set to `all`. If need be, `$type` may be set to false to ignore media type.
- Under the `function`s, the `$type` isn't set. If need be, `$type` may be set to whatever feature, type, or state you need.
Added a test for comma-separated lists of media queries. Related to #2

Note :
- Also updated `$mq-breakpoints` to `$mq-horizontal-breakpoints` to match new syntax.

Todo :
- Add vertical media query tests.