Background position limits

[juliangut]

Problem

Fully move background image within container limits.
Using "bound: false" and "background-repeat: no-repeat" you can move the image out of sight.

Solution

Limit background movement to prevent getting out of sight.
Additionally adding an inner frame to constraint how close to the borders can the background get, allowing the image to be always be visible at least those pixels

Implementation

New option "frame" indicates number of pixels to limit background movement. Only used when "bound: true"
Frame option is best viewed with "background-repeat: no-repeat"
Calculate boundaries for background position when "bound: true" and a frame is provided so you can move background freely inside container boundaries limited by frame.

Extra

The ability to trigger drag from inner elements (in the example from <p> elements) is desirable in some situations. Added a "propagate" option for this

[juliangut]

It's been months since @bcole808 and my PR (January) so sorry to ask this but, are you still managing this library?