Allow dollar in symbol names

[emanspeaks]

Some language dialects allow dollar signs in symbol names. In Intel, this is always allowed. In g77, it can be enabled via command line flag. This seems to be an older practice that has fallen out of favor and was always a language extension, but is needed to support backward compatibility with older codes.

I've opted to implement this as always allowed like the Intel implementation, but I can change this to be an opt-in feature if we'd rather. I don't suspect it will hurt anyone to allow it.

There are other noted historical uses of $ in Fortran that are more rare, particularly with different variations of write statements, but it is unclear if any of these are still supported today by any compilers. (Even if they are, the current proposed regex is unlikely to erroneously match to them.)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (8466034) 87.52% compared to head (7a31879) 87.52%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #351   +/-   ##
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  Coverage   87.52%   87.52%           
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  Files          35       35           
  Lines        4760     4760           
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  Hits         4166     4166           
  Misses        594      594           

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[gnikit]

LGTM. Thansk for the PR.

Having the option on by default for me is the way to go. I think you know my stance with weird (possibly deprecated) compiler extensions; they should really not be part of modern day tooling. This one however seems to be minimally invasive and I can't see any side effects so all is well.