Styleguide & Conventions

**Do not accept this PR until discussion below has reached an agreement and all changes have been finalized.**

Carefully read the items on the list and voice your opinion on any item you feel needs changing. If you feel there are missing items, wait for this PR to go through and then submit your own PRs.

**Styleguide:** https://github.com/LB--/ChessPlusPlus/tree/master/src#readme