Support maxAge query parameter to Shields.io in badge redirect

[wmayner]

Details

Shields.io allows passing a maxAge query parameter that should address #1612, but this is not supported by the RTD redirect.

Expected Result

The Location header from curl -v https://readthedocs.org/projects/pyphi/badge/?version=latest&style=flat-square&maxAge=600 should be:

Location: https://img.shields.io/badge/docs-latest-brightgreen.svg?style=flat-square&maxAge=600

Actual Result

maxAge is ignored, though style is respected.

The Location header from curl -v https://readthedocs.org/projects/pyphi/badge/?version=latest&style=flat-square&maxAge=600 is:

Location: https://img.shields.io/badge/docs-latest-brightgreen.svg?style=flat-square

[ericholscher]

This would be a great contribution! The code is here: https://github.com/rtfd/readthedocs.org/blob/master/readthedocs/projects/views/public.py#L119

[wmayner]

Implemented in PR #3005.