Installation Fails

[nfarrar]

Installing on OSX 10.10 with homebrew python 2.7.8:

$ pip install vimdown
Downloading/unpacking vimdown
  Could not find any downloads that satisfy the requirement vimdown
  Some externally hosted files were ignored (use --allow-external vimdown to allow).
Cleaning up...
No distributions at all found for vimdown

$ pip install vimdown --allow-external ... --allow-external option requires an argument

After some googling, this seems to be due to a change in pip. I tried the following as well, which results in build exceptions.

$ pip install vimdown --allow-external vimdown --allow-unverified vimdown
$ pip install vimdown --allow-all-external --allow-unverified vimdown

Same errors when attempting to install inside a virtualenv.