Allow fetching repos file from URL

[christophebedard]

Supersedes and addresses review feedback from #123

I added a simple test, but the actual request could probably easily be mocked (#103).

[dirk-thomas]

Thanks for picking this up. Please see a few comments / questions inline.

[dirk-thomas]

Thanks for the updates. I made two minor changes:

• moved the new function around, condensed the lines a bit and renamed the function argument from x to value and
• reverted the unrelated default value change (I will create a separate PR for that which addresses the same in another place too)

[christophebedard]

looks good!