Add serialization to be able to save/load games

[SuperFola]

I'm currently trying something on this branch, but before going further, maybe one should consider trying a premade library for this, like cereal

The goal is to be able to serialize:

• the player
• the player attributes: attack, defense, bags and the objects in it, its position, health and such
• the objects we picked up, so that they aren't regenerated when the game starts again
• the terrain modifications (if any, currently we don't support it), if the player destroyed a wall or whatever (can be skipped for now)
• the seed of the random number generator (we should use the same seed everywhere or the same RNG, to generate the same map)

[HexDecimal]

Cereal is on Vcpkg. It should be easy to add it to the Vcpkg manifest and the CMake scripts.

[gusmccallum]

Hi I'd like to work on this, please assign it to me.

[SuperFola]

Ok!

[gusmccallum]

Thanks!

[SuperFola]

I've picked up the issue again, correcting your code @gusmccallum.

This does compile now, but there are a few blocking things upon saving (and most likely when loading as well).