Make access to qgamma and friends easier

[kcrisman]

See this discussion about plotting and using qgamma.

sage: var('q,x') 
sage: from mpmath import qgamma 
sage: plot3d(lambda q,x: qgamma(q,x), (q, 0.5, 3), (x, 2, 10)) 

Component: symbolics

Branch/Commit: u/zonova/make_access_to_qgamma_and_friends_easier @ 360823b

Issue created by migration from https://trac.sagemath.org/ticket/19032

[sagetrac-zonova]

Branch: u/zonova/make_access_to_qgamma_and_friends_easier

[sagetrac-git]

Commit: 360823b

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

360823b

Adding comments to the code