add Hashable instance for Options SVG R2 (and remove Show)

unfortunately we also have to add some orphan Hashable instances for
blaze-markup types.  We could contribute them back upstream to
blaze-markup, but that would require adding a hashable constraint.
actually remove Show (Options SVG R2) instance
clean up warnings
Merge branch 'master' into builder-cleanup
Merge pull request #45 from diagrams/builder-cleanup

Add Hashable instance for Options SVG R2