Comparing `vimCommand` from Vim's runtime/syntax/vim.vim, one can see
that "augroup" and similar commands are conspicuously missing. They are
handled specially (`vimAugroupKey`, `vimAutoCmd`).
Excluding them from the generated `vimCommand` keyword list, fixes their
highlighting.
closes#9327
Removes all kinds of problems with sorting, provides a ready-to-use function
list representation for genvimvim.lua, does not require specifying function name
twice (VimL function name (string) + f_ function name).
