feat(core): Add lua modules

[dranikpg]

Add the following modules to the lua interpreter:

• cjson
• cmsgpack
• struct
• bit

and registers them in the globals table.

Helps with #184

[dranikpg]

I've chosen to embed the module sources at src/redis/lua because:

• the build process of cjson/cmsgpack would have to be patched significantly
• bit/struct are standalone and would require a build solution on their own

I guess, a single target with a single build file at src/redis/lua would be enough? The other option would be fully subdividing everything and listing all the modules in a cmake variable.

[romange]

Looks good.

1. A single target is fine.
2. We need tests inside interpreter_test that cover the functionality of all modules
3. If you had to change the original files - please add a readme explaining in a few lines what had to be changed or provide a patch snippets (whatever is simpler).

[dranikpg]

I've fixed the registration process, because lua 5.2 changed the way modules are registered. (lual_register became deprecated https://www.lua.org/manual/5.2/manual.html, the new luaL_newlib doesn't make it global upon registration to be used with require instead)

The modules show quite a lot of warnings (about 20) during compile (mainly sign-compare, implicit-fallthrough, misleading-identation). Should I fix them or just suppress them in the sub-build?

[romange]

just opress them - see target_compile_options in redis CMakeLists

[romange]

do you mind squashing the commits into a single one?

[dranikpg]

forgot to pull my merge 😓