change type of arrow gaps to Measure R2
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