perf(api): allow to use an arena for return values

- add section for managing includes via IWYU
- recommend clangd over ctags
- tidy up links
- remove ./scripts/check-includes.py

vim-patch:8.1.1927: code for dealing with script files is spread out

Problem:    Code for dealing with script files is spread out.
Solution:   Move the code to scriptfile.c. (Yegappan Lakshmanan, closes vim/vim#4861)
https://github.com/vim/vim/commit/307c5a5bb77c3728dfab06c30e9f786309c63f74

Problem:    Profiling functionality is spread out.
Solution:   Put profiling functionality in profiling.c. (Yegappan Lakshmanan,
            closes vim/vim#4666)
https://github.com/vim/vim/commit/fa55cfc69d2b14761e2a8bd85bc1e0d82df770aa

Move proftime_T to types.h for now to avoid recursive #include.

The targets will only format files that have been changed in current
branch compared to the master branch. This includes unstaged, staged and
committed files.

Add following make and cmake targets:
formatc   - format changed c files
formatlua - format changed lua files
format    - run formatc and formatlua

Remove scripts/uncrustify.sh as this deprecates it.

The last commit didn't actually disable V1028 because of a typo.
Fix the typo so it is actually disabled.

Most casts where PVS warns for V1028 aren't added to prevent overflows
in the first place, but to avoid other warnings, like printf argument or
-Wconversion warnings. PVS/V1028 is more annoying than useful.

It currently falls back to texlua if luajit doesn't exist. However,
the documentation generation does not work with texlua. Instead use lua
as a fall back instead.