[mod] add ordering to Position
[mod] allow exportation of type BoundingBox
[mod] make properties of left and right
[mod] add validity test to Position
[mod] uniformise Position and BoundingBox API

The classes constructors are used when you give explicitly the
arguments, the make_* functions are used when you're not sure of the
type of your argument
[mod] add total_ordering for python 2.6
[mod] merge APIs for Position and BoundingBox
[doc] update changelog
[mod] add repr to BoundingBox
[mod] do not use exceptions for normal behaviour
[mod] explicit failure in constructor
[doc] enhance documentation
Merge remote-tracking branch 'origin/pathuniformisation'

Conflicts:
	CHANGELOG
	tests/test_path.py