Throw a syntax error in the current position
@param {string} message
@param {number} [errorLine=line]
@param {number} [size=1]
@throws {SyntaxError}
@private
function throwSyntaxError(message, errorLine, size) {
		errorLine = errorLine === undefined ? line : errorLine
		size = size === undefined ? 1 : size
		var snippet = getSnippet(source, errorLine, size),
			err = new SyntaxError(message + '\n' + snippet)
		err.line = errorLine
		throw err
	}