Merge pull request #13 from braxton-schafer/develop

Develop
Merge branch 'master' of https://github.com/braxton-schafer/pyberry

* 'master' of https://github.com/braxton-schafer/pyberry:
Merge branch 'develop'
Merge branch 'develop'
Merge branch 'develop'
Merge branch 'develop'
Add error checking to "Add by title" to handle nonexistent authors

Occasionally Google Books will show no author for an item, which would cause a crash with a KeyError.  This catches the exception and allows execution to continue.

Close #19
Fix issues with 'Add by ISBN' to get rid of this pesky crash.
Merge branch 'hotfix/0.9.1' into develop