Introduce new build type Dev that replaces RelWithDebInfo for development
builds off master and has optimizations, debug info, and logging enabled.
Keep assertions enabled for RelWithDebInfo.

This doesn't prevent compilation of jemalloc, but the important thing is
that it prevents it being used in nvim.

refs 6cd20177df9d675c4c8de9ae27ce8c0ea2a94cca
refs 95707bf336794c7ec8991917f184c02ae873dd8c

What works:

1. ShaDa file dumping: header, registers, jump list, history, search patterns,
   substitute strings, variables.
2. ShaDa file reading: registers, global marks, variables.

Most was not tested.

TODO:

1. Merging.
2. Reading history, local marks, jump and buffer lists.
3. Documentation update.
4. Converting some data from &encoding.
5. Safer variant of dumping viminfo (dump to temporary file then rename).
6. Removing old viminfo code (currently masked with `#if 0` in a ShaDa file for
   reference).

DUSE_JEMALLOC was removed in 8130eb1191aece52d8b2790302abf1bd09aaf90f

Helped-by: Florian Walch <florian@fwalch.com>
Helped-by: John Szakmeister <john@szakmeister.net>

- Mention how to disable jemalloc during compilation
- Mention using additional CFLAGS during compilation

This library makes it easier to script communication with interactive programs.
It is similar to what the "expect" tcl extension does, but uses an object
oriented API and is designed to integrate nicely with Neovim job control.

[ci skip]

[ci skip]