Use tox
Create pth files for existing projects.
Move CWD to the top of sys.path.

This favors your CWD items over items you've checked out.

E.g. a directory like

```
~/code/
    foo/
        tests
    bar/
        tests
```

If you are in `~/code/foo` and do `import tests` you will get `foo`'s
tests not `bar`'s tests.
Merge pull request #5 from davedash/install-repo

Some fixes for install-repo: