Support "inside" and "outside" stroking of paths

[Sébastien Pierre]

In other vector tools, it is possible to select how a path stroke is rendered. Inkscape's defaut is to render the stroke so that the path is always at the middle of the stroke. This can be quite problematic when working with grid-assembled rectangles, where you want to avoid the stroke bleeding out of the actual shape (which is the case with current stroke preset). Here is an illustration of the two other ways of stroking that would be useful:

Inkscape default (middle stroke):
============ [STROKE]
-------------------------- [PATH]
============ [STROKE]

Inside stroke:

-------------------------- [PATH]
============ [STROKE]
============ [STROKE]

Outside stroke:

============ [STROKE]
============ [STROKE]
-------------------------- [PATH]