Changed the overlap algorithm to use the plane sweep technique for
finding intersections and remove overlapping curves.
Use generic curve when possible.
Merge branch 'master' of github.com:kuribas/fontforge.github.com into kuribas-master
Merge branch 'kuribas-master'
Merge branch 'master' of github.com:fontforge/fontforge.github.com

Conflicts:
	en-US/documentation/reference/overlap.md