PLSyntaxHighlighter no longer throws exceptions; instead, it logs errors.
Added error domains and codes for Liasis and LiasisKit.
The two Python conversion categories now use NSError instead of exceptions.

NSArray+pythonList and NSDictionary+pythonDict have altered methods that take
an NSError** pointer, populate it when an error occurs, and return nil in
this case.
Converted methods using the Python conversion methods to use their errors.

These are in PLSynaxHighlighter and PLPythonIntrospectionController. All methods converting Python objects now handle the error cases and return an error through the NSError** argument.
Updated methods interfacing with the introspection controller and syntax highlighter.

This affects the PLEditorViewController and PLInterpreterController classes. The former calls presentError: when it gets one. PLInterpreterController does not yet have a mechanism for calling presentError: so it currently logs the error instead.
PLEditorViewController now handles when init fails in PLSyntaxHighlighter and PLPythonIntrospectionController.
Merge branch 'feature-errors' into develop

The merging branch replaces exceptions with NSError handling when interfacing with Python.

Conflicts:
	Liasis/Liasis/Categories/NSArray+pythonList.m
	Liasis/Liasis/Parser/NSDictionary+pythonDict.m
	Liasis/Liasis/Parser/PLPythonIntrospectionController.m
	Liasis/Liasis/SyntaxHighlighter/PLSyntaxHighlighter.m
	Liasis/Liasis/TextEditor/PLEditorViewController.m