[MacPorts] #42273: Support release downloads in GitHub portgroup

[MacPorts]

#42273: Support release downloads in GitHub portgroup
-------------------------+--------------------------------
 Reporter:  bgilbert@…   |      Owner:  macports-tickets@…
     Type:  enhancement  |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  base         |    Version:  2.2.1
 Keywords:  haspatch     |       Port:
-------------------------+--------------------------------
 After deprecating the "downloads" system for release tarballs, GitHub
 later reinstated the ability to upload tarballs via the "releases" system,
 which uses different URLs.  Allow portfiles to specify
 `github.tarball_from releases` to set `master_sites` appropriately.

 These ports currently have `master_sites` pointing at the GitHub releases
 system:

 - python/py-ipython
 - python/py-sympy
 - science/erfa

-- 
Ticket URL: <https://trac.macports.org/ticket/42273>
MacPorts <http://www.macports.org/>
Ports system for OS X