Consider making brackets-beautify work with multiple selections

[njx]

As mentioned in #52, we're adding multiple cursors/selections to Brackets in Sprint 38. Since brackets-beautify operates on the current selection, it might make sense for it to work with multiple selections (i.e., if there is a multiple selection, beautify each of the selections).

For general info on how to make edits work with multiple selections in Brackets, please see Changes to Editor selection APIs and Performing edits on multiple selections. Also, if you do start taking advantage of these APIs, please make sure to mark your new version as requiring sprint 38 by setting "engines": { "brackets" : ">=0.38.0" } in your extension's package.json.

Thanks!