templater: use templatefunc to mark a function as template function Using decorator can localize changes for adding (or removing) a template function in source code. This patch also removes leading ":FUNC(ARG...):" part in help document of each function, because using templatefunc makes it useless. This patch uses not 'func' but 'templatefunc' as a decorator name, because the former is too generic one, even though the latter is a little redundant in 'templater.py'.