Wrong sign in HeatTile.get_ll_bounds padding

[gusajz]

The method substracts the padding from self.top and adds it in self.bottom, but it should be the other way. According to google maps documentation (https://developers.google.com/maps/documentation/javascript/maptypes#WorldCoordinates), Y coordinates go from north to south (ie: increasing going to north).

This causes, that padding actually make the box smaller, instead of larger, in the y axis. The result is a gap in top and bottom borders of every tile.

Actual code:
def get_ll_bounds(self, padding=0.0):
(n, w) = self.px2ll(self.left - padding, self.bottom + padding)
(s, e) = self.px2ll(self.right + padding, self.top - padding)
return (s, n, w, e)

Proposed fix (note the signs in px2ll second argument):
def get_ll_bounds(self, padding=0.0):
(n, w) = self.px2ll(self.left - padding, self.bottom - padding)
(s, e) = self.px2ll(self.right + padding, self.top + padding)
return (s, n, w, e)

[amccollum]

Sorry for the slow response. I'm willing to believe you're right on this if you've tested it. Can you submit a pull request? Thanks.

[gusajz]

Yes, I've been using it intensively. Sure, I'll submit a pull request :)