Fix uci isready, ucinewgame

[znxftw]

The uci command isready is supposed to return readyok once the engine has finished initializing.
This was initially trivial, the number of initializations / clearing of memory was not significant.
If we want to make our engine better we need to add some extra checks - Transposition Tables should be initialized, move history should be cleared (possibly force GC?) and all static members need to be initialized.

Return readyok only once everything is done.

Abstract out proper ways to know "are we done initializing" so that future code coming in can easily say "I'm not done yet" instead of rewriting the entire isready logic everytime.

ucinewgame also needs to be revisited - clear everything, make sure this also unsets readyok until it's done

[znxftw]

Relates to #12