Return selection start and end DOM elements

• return the selection start and end DOM Elements
• better handling of clicks on the menu

Support Firefox textareas and the selection ending outside the container

• Firefox support for textareas
• display the menu even if the selection ends outside the container (#8)
• clearer mouse event handling
• more test cases

Textarea handling, better menu hiding, better CSS isolation

• handle selection in textareas, though imperfectly without textarea-caret-position
• reset CSS more robustly with all: unset
• hide the menu according to browser selection clearing vagaries
• 3D shadow

Drop Drop, use Tether directly

The dependency on Drop has been dropped, and now we use HubSpot's Tether directly. This was motivated by a number of insidious bugs in the Chrome extension, which are thus solved.

menuHTML has also been deprecated in favor of content (similar to Drop's content option).

Switched to HubSpot's Drop library

SelectionMenu now uses HubSpot's Drop library for better positioning.

This is a pre-release because we plan to drop Drop and use Tether directly (on which Drop is based).

Last release before switching to HubSpot's Drop

This release still uses the original naive positioning of the menu.