REPP mismatches with inline flags

[goodmami]

There are some REPP rules that use inline flags, such as (?i) in the following rule:

!Β|&#((?i)x392);|Β		Β

With Python's re module, inline flags affect the whole pattern and not just the sub-pattern, so this would match β as well as Β. PCRE does treats inline flags as local to their group, so it would match Β and not β. The 3rd-party regex module of Python is more like PCRE, so we could possibly resolve the issue by using that module if it's available.

[goodmami]

Using the regex module fixes the issue at hand but raises another: nested sets. Currently the ERG's REPP system fails to load at all with regex because of unescaped brackets in a character class. See delph-in/erg#17.

[goodmami]

Fixed by de6e616