Basic class structure for PuiseuxSeries.

The basic class structure now exists for Puiseux series.
Operations with symbolics works but substitutions don't
evaluate to PuiseuxSeries.
Merge branch 'puiseuxclass' of github.com:cswiercz/abelfunctions
Checkpoint analytic continuation fix.
Fix intersection number computation.

Intersection numbers were improperly computed. Certain
cases were missed.
Detabify some files.
Untabify and delete trailing whitespace in monodromy.py
Merge branch 'master' into ancont
Untabify and delete trailing whitespace in riemannsurface_path.py
Analytic continuation seems to work again.