vim-patch:8.0.1206: no autocmd for entering or leaving the command line
(commit a4f6cec7a3)
NA patches:
vim-patch:8.0.0320: warning for unused variable with small build
It's important that users have a single, easy-to-remember place for
reading about the API. So this commit changes gen_api_vimdoc.py so that
the generated section is appended to api.txt instead of creating
a separate document.
Also remove the section numbering and ToC: it's a maintenance cost, and
it will be unnecessary when #5169 is integrated.
