[visibility] Bresenham's line algorithm

Implementation + unit test.
Add (x,y,z,theta) point
Robot model handles sensor position.

Namely sensor's (x,y,z,t) relative position.
[Visibility] Visibility link between two points
[Visibility] Unit test.
[visibility] cleanup previous commits
[visibility] store heightmap reference localy
[test] fix new robot sensor model update
[gladys] add is_visible and can_communicate (same)
Bump to v0.1.5
Prepare for v0.1.6
[visibility] fix after Arnaud comments
[tool] add rpkg comment and sed
[visibility] add robot_model.senor.range
[visibility] add bench visibility and fix test
[visibility] add bench visibility comment
[gladys] Update API
Bump to v0.1.6
add some comment