support note id calculation (William Casarin)

extract cursor_push_unescaped_char (William Casarin)

add sha256 (William Casarin)

test: add test that make sure string functions work before finalization (William Casarin)

builder: allow note string funcs to work before finalization (William Casarin)

Add a CMake script. Tested in Ubuntu Linux 22.04 (pvn)

pushed to nostrdb:refs/heads/master

http://git.jb55.com/nostrdb/commit/4e75ac71c34124e04b9e726e78418129cb159f4b.html