Added instructions for migrating to Breakpoint 2.x or staying at Breakpoint 1.x

[lolmaus]

bundle update has broken my project today.

It took me some time to figure things out. I've added instructions for migrating to Breakpoint 2.x or staying at Breakpoint 1.x.

[Snugug]

With the exception of the deprecated $media, $no-query, and $base-font-size input options (deprecated in Breakpoint 2.0), the current version of respond-to is fully compatible with Breakpoint 2.0 with both its legacy syntax option and its new syntax. We are still in the process of documenting Breakpoint 2.0, so this is a little bit premature at the moment.

[lolmaus]

The Respond To gem calls breakpoint like this:

@include breakpoint($mq, $media, $no-query, $base-font-size)

Whereas the corresponding mixin in Breakpoint 2.x is defined like this:

@mixin breakpoint($query)

Which results in crashing a project with a "wrong number of arguments" error.