Add default instances for LineJoin and LineCap.
Adding offsetTrail and expandTrail.

These use the offestSegment function to build and offset for a whole
trail or expand a trail as though it was stroked with a particular line
style.  Still needed are documentation and an implementation of miter
join.
Adding documentation for offsetTrail and expandTrail.
Add more documentation and miter join.
Merge branch 'master' into expand
Working on offset Loops.
Missed some handling of loops last time.
Merging.
Loops now working.  Code could use some refactoring.
Merge branch 'master' into expand
Updated for diagrams-haddock changes.
Merge branch 'parametric-Located' of github.com:diagrams/diagrams-lib into expand
Fixed Offset for new instance for Codomain (Located a).
Merge pull request #103 from diagrams/expand

Add offsetTrail and expandTrail.