Review Exception Types

[Byron]

Currently, whenever something git-specific happens, git-python will throw a more or less generic Python exception, such as ValueError or TypeError, including a very git specific message though.

Client Code is less readable that way, as it will handle these general exceptions very specifically although this is not indicated by the exception type.

Review the all raise statements and introduce custom Exception types which are derived from the type you currently see. This way client code will be more readable without breaking existing code.

[Byron]

When looking through half of all the exception thrown by git-python, I couldn't find a single one that would be too generic or not matching the situation in which they have been thrown.
Therefore I believe it's safe to assume this issue is old enough to not be relevant anymore in the current code base.