Added jrnl formula

Hi there, 

I added a new formula for [jrnl](http://maebert.github.io/jrnl/) following your `contributing` guidelines.
It installs on a mavericks host and runs the test correctly.

If possible, please merge.

Thanks for your work.
Ok, I tried this and smashed against this:

```
...
==> python setup.py install --prefix=/usr/local/Cellar/jrnl/1.9.5
running install
Checking .pth file support in /usr/local/Cellar/jrnl/1.9.5/lib/python2.7/site-packages/
error: can't create or remove files in install directory

The following error occurred while trying to add or remove files in the
installation directory:

    [Errno 2] No such file or directory: '/usr/local/Cellar/jrnl/1.9.5/lib/python2.7/site-packages/test-easy-install-35164.pth'

The installation directory you specified (via --install-dir, --prefix, or
the distutils default setting) was:

    /usr/local/Cellar/jrnl/1.9.5/lib/python2.7/site-packages/

This directory does not currently exist.  Please create it and try again, or
choose a different installation directory (using the -d or --install-dir
option).
```

My changes are:

- remove the Dir line
- change the jrnl "setup.py" line to aim to prefix=#{prefix}

I think that jrnl installs stuff in the python path and for some reason this is not being installed in the right path.

What do you think about this?