add a Renderable instance for ScaleInv
new function scaleInvPrim for creating a diagram from a single scale-invariant primitive
further clarify intention of scale-invariant primitives
Merge branch 'master' into scaleinv-prim

Conflicts:
	src/Diagrams/TwoD/Transform.hs
add IsPrim instance for ScaleInv
add IsPrim instances for Path, Ellipsoid, Image, and Text
typo fix in IsPrim instance for ScaleInv
add more comments re: ScaleInv in Diagrams.TwoD.Transform
Merge branch 'master' into scaleinv-prim
Merge pull request #71 from diagrams/scaleinv-prim

New `scaleInvPrim` function
Added offsetSegment function that builds a trail that is a fixed distance from the original segment.
Bumped upperbound on numinstances.
Added images for haddock.
Merge pull request #79 from diagrams/offset

Added offsetSegment function
clean up pragmas, imports, and whitespace in D.TwoD.Arc
Merge branch 'master' into arrows
clean up imports/pragmas in D.TwoD
start work on arcBetween function for drawing arcs between two given points