remove FillColor and LineColor attributes
remove headColor and friends
minor edits
merge master
fix handling of text scaling

Fixes #179.  This patch is very much along the lines outlined in
comments on the ticket.  There will be accompanying patches to backends.
Merge pull request #182 from diagrams/text-scale

fix handling of text scaling
Update Attributes.hs

We will probably have to continue to adjust these over time until we converge and the best values.
Adjust size nicknames
merge in master
add solid
fix arrowheads joint scaling
Joint opacity needs to be set.
Rewrite arrowheads to be a function of head length
Merge branch 'master' into arrow-length
generalize spike to arbitrary angles
convert tails to be a function of length
added lengths travesal
fix haddock diagrams
more haddock diagram corrections
Allow semigroups-0.14