Set title to a non-empty string to avoid crashes

[andrewhavens]

This pull request changes the behavior of setting the title key in the cell hash to an empty string. Fixes #42

Changed:

• App no longer crashes when title is nil or set to ''. It defaults to ' '

  Added:

• Additional documentation around specifying properties

[kevinvangelder]

:+1:

[jamonholmgren]

Yay!