Add luacheck

[OgelGames]

Added luacheck and fixed most of the warnings, but there's a few harder ones to fix.

• [ ] Line length warnings: (could change max_line_length to 180, but better to fix them)

  api.lua:499:121: line is too long (146 > 120)
  api.lua:700:121: line is too long (133 > 120)
  api.lua:705:121: line is too long (157 > 120)
  api.lua:920:121: line is too long (123 > 120)
  api.lua:1074:121: line is too long (124 > 120)
  api.lua:1119:121: line is too long (131 > 120)
  api.lua:1122:121: line is too long (146 > 120)
  api.lua:1149:121: line is too long (129 > 120)
  api.lua:1246:121: line is too long (177 > 120)
  api.lua:1270:121: line is too long (131 > 120)

• [x] Assignment warnings:

  encoding.lua:281:6: right side of assignment has less values than left side expects
  encoding.lua:293:4: right side of assignment has less values than left side expects
  encoding.lua:297:5: right side of assignment has less values than left side expects
  encoding.lua:307:5: right side of assignment has less values than left side expects
  encoding.lua:320:6: right side of assignment has less values than left side expects

https://github.com/mt-mods/signs_lib/blob/3f1a8fa3f25a17bc33f700bb249627d3f11c7f8d/encoding.lua#L281

@syimyuzya what is intended with those assignments? Should both variables be assigned the value, or only one?

[OgelGames]

I decided to just increase the max_line_length for now, the code needs some refactoring to make some of those lines shorter, and it's better to leave that for when all the code gets refactored. (it really needs it...)