Step 1 - eliminate Split monoid and freeze
fixed merge conflicts
initail measure work
Merge branch 'master' into units
enable merege
working - no arrows
convenience functions
Global working
changes to accomodate refactored backend class
remvoed IsPrim
arrows working without scaleInv
changed default arrowhead size
updated ArrowTest.hs
line width nick names
make arrow HeadSize & TailSize Attributes

as Attributes, they can be defined in terms of Measure, and easily
converted to Output during rendering
add new module Diagrams.TwoD.Compile for rewriting RTree, to avoid
import loop
add Diagrams.TwoD.Compile
express FontSize using Measure
change type of toOutput to pass into toRTree
added default instances of HeadSzie and TailSize
Fix modifyStyle

I think this should fix the crash of `headSize (Global t)`
but I'm not at a computer where i can compile the code.
D.TwoD.Adjust: return transformation from adjustment functions

Also change adjustment functions to take a lens rather than a
getter/setter pair.