Merge pull request #660 from bvssvni/master

Moved `Has` traits to own module
Merge pull request #662 from bvssvni/master

Moved `Can` traits from internal to its own module
Merge pull request #672 from bvssvni/master

Made library compilable with `f32`
move translate to take vec2d as arg
Merge pull request #673 from bpicolo/move_translate_to_vec2d

move translate to take vec2d as arg
line_side to vec2d arg
inside_triangle to vec2d arg
relative_rectangle to vec2d
move separation to vec2d arg
move shear to vec2d arg
Merge pull request #674 from bpicolo/change_args_to_vec2d

Change args to vec2d
Add cells() iterator for grid
Merge pull request #675 from bpicolo/636_add_cells_iterator_for_grid

Add cells() iterator for grid
Fixed doc comment

Closes https://github.com/PistonDevelopers/graphics/issues/676