Fix a highlighting problem with nested braces

Due to a bug in Vim (or more likely, a misunderstanding on my part),
I had to remove the transparent property from the following regions
in order to get them to highlight correctly.  Feel free to remove
these and reinstate the transparent property if you know how.
Make sure hash access in interpolated strings works right

Expressions like $hash{$var} weren't being properly considered
in nesting of forms like qq{...}

This closes GH #73