rivet.AOPath raises a raw Exception instead of being more specific

This is more of a feature request rather than a bug but inside the constructor of rivet.AOPath, an Exception is raised when there is no regex match. Catching a raw Exception is considered bad practice and a better alternative would therefore be to raise a more narrowly defined exception, such as ValueError. The code will still mostly be backwards-compatible, since ValueError inherits from Exception, so user-written code of the form

try:
    rivet.AOPath(something)
    ...
except Exception:
    ...

will still work.

I can try to make a merge request that replaces Exception with ValueError at some point in the near future, if this is desired.