Process a list of simple string field definitions and assign their order based on prefix.

def process_fields(self, fields):
		"""Process a list of simple string field definitions and assign their order based on prefix."""
		
		result = []
		strip = ''.join(self.PREFIX_MAP)
		
		for field in fields:
			direction = self.PREFIX_MAP['']
			
			if field[0] in self.PREFIX_MAP:
				direction = self.PREFIX_MAP[field[0]]
				field = field.lstrip(strip)
			
			result.append((field, direction))
		
		return result