Virtualenv-api

* 29: Fix AttributeError when raising OSError from inside environment (rmb938)

* 28: Add support for locating pip on win32 (eoghancunneen)

* 27: Support installing an editable package (`-e`) (sjkingo)

* Move version number to library instead of `setup.py` (sjkingo)
* Support Python 3.5 (sjkingo)
* 24: Fixed failing test suite by adding missing dependency (mcyprian)

* 21: Converted `README.md` to an rST document to remove dependency on
`setuptools-markdown` (sjkingo)

* Added `upgrade_all()` function to upgrade all packages in an environment (sjkingo)
* Added `readonly` argument to constructing environment that can be used to prevent
operations that could potentially modify the environment (sjkingo)
* Added support for passing ~ to construct environment (e.g. `~user/venv`) (sjkingo)