Return capability by its name

		:param cap_name: name of a capability to return
		:return: bounded method or None (if a capability is not found)

def capability(self, cap_name):
		""" Return capability by its name

		:param cap_name: name of a capability to return
		:return: bounded method or None (if a capability is not found)
		"""
		if cap_name in self.__class_capabilities__:
			function_name = self.__class_capabilities__[cap_name]
			return getattr(self, function_name)