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.
The bad thing is that when this app starts creates a ~/.jrnl_config file where it stores some information (like the journal file) provided by the user. 
If we force jrnl to actually do something that would probably alter/trash the user's configuration (say you update it and want to check that it works).
I think it should be possible to add a self-test function to the app (which actually makes sense) to make sure that it actually works ok. But for the time being making sure that the app launches ensures that at least you can have an unencrypted file.