+ShortMessage property.
+WriteAllLines method for IFileAdapter and basic impl.
+Save method that writes the short message to the path. +Test
+ICommitDocument interface.
CommitDocument now implements its new interface.
App class now holds a reference to an ICommitDocument.
Now saves the commit document on Enter press. +Test
Real implementation for FileAdapter.WriteAllLines.
+ShortMessage property to ICommitDocument.
Stores the entered commit text onto the document before saving. +Test