See frama-c/frama-c#1364

- no more casts inserted in front of the litteral
- use actual `'c'` value (or `L'c'` for wide char) instead of numerical one

Update tests: WP now populates exits and terminates

See merge request frama-c/frama-clang!220

More robust build instructions

See merge request frama-c/frama-clang!217

Feature/martin/kernel/add loc argument for populate spec

See merge request frama-c/frama-clang!219

Feature/kernel/default spec

See merge request frama-c/frama-clang!214

[userman] much needed update

See merge request frama-c/frama-clang!218

- convert to new frama-c-book class
- fixes incoherent use of macros (probably some more work to do)
- update instructions post-dune migration
- announce opam package

This will allow the opam package to export whatever conf-llvm has found, so that
we don't have to guess ourselves all the variations that some random
LLVM package manager has come up with at some point.