[analyzer] A quick manual for checker developers

For a while, we've been using this manual in our small project, for
newcomers and as a reference guide. Now we've got a chance to share
it, so i made it a bit more appropriate for the official clang, and
put on github. That's around 60 pages, with a lot of hand waving, some
code snippets, alphabetical index, and references to fancy stuff.

Direct download for the early release:
    https://github.com/haoNoQ/clang-analyzer-guide/releases/download/v0.1/clang-analyzer-guide-v0.1.pdf

Source code:
    GitHub - haoNoQ/clang-analyzer-guide: An easy guide to Clang Static Analyzer extension.

There's still a lot to fix. One major thing is we're stuck on an old
version of clang, so there's quite a bit of updates needed to the code
style in samples. Shouldn't take long, but still a to-do. Apart from
that, there's a big to-do list of smaller stuff to fix right in the
front page of the guide.

We decided to make the guide in LaTeX/PDF because we wanted it to be
printable, but as such it may not be easily integrated into the
existing docs at llvm.org. Not sure - if it's found to be worth it
some day, then i'd look into converting it.

I've picked the CC-BY v4.0 license; this is not set in stone, i'm not
good at laws, so i might have missed something, so if anybody sees any
issues with that please report. Anyhow, i don't intend to restrict
sharing and modifying this documentation etc.

Last but not least, the guide is written in my very poor English, for
which i heartily apologize!

Anyway, despite all that, it might anyway be a useful reading, and we
can probably finally have something to give to people who ask for more
docs. And i hope to keep fixing stuff.

Best regards,
Artem.