added invert feature to follow sprites instead of avoid them
refactored adding nodes to open list, added check for tile map edges
tests for TileMap.findPath() added, findPath refactored and invert mode added.
changed edge to return current cell, path list now returned as x, y co-ords rather than [col,row] indexes

tests update and added an extra test to describe what happens when
start and end point are the same.
initial implementation of lineOfSight() function

test placeholders included but not implemented
implemented inverted version of lineOfSight(), tests added
updated example for tilemap changes, added LoS, rebuilt

Added Line of Sight to the example, second character hiding in the
'cave' can only been see when there are no walls betwen it and the
player.
Merge pull request #62 from MalphasWats/master

Tests for TileMap.findPath() added, inverted feature added and a bit of tweaking