POC: alphabetic constants
* New priority for alphabetic characters
* Overloaded OperandNode constructor
* Currently not usable, only basic proof of concept
Merge branch 'master' into feature_constants

Conflicts:
	src/tree.cc
	src/utils.cc
Switched OperatorNode to TokenType
* OperatorNode class now uses TokenType for internal operator storage and logic selection
* print-Method resolves the TokenType back into its character representation
Merged Node factory-methods into template method
Added ConstantNode blueprint
Enabled C++11 for clc and test applications
Implemented constant identifier functionality
* SimpleParser optionally acceps a pointer to an ConstantMap containing string keys mapping to values
* Constants are handled in their own ConstantNode class derived from the standard Node class
* Operator precedence is now determined separated from the TokenType using a new PrecedenceLevel enum
** Conversion between tokens and their PrecedenceLevel is possible using the new utility function getPrecedence
* Added additional test cases for constant identifier resolutions