Block-breaking time with block hardness (vs instamine)

[satoshinm]

Currently blocks break instantly when right-clicked. This is fine for "creative mode", but for an engaging survival experience, blocks should vary in hardness and some take longer to mine, where you have to click and hold to complete the mining process.

Interacts with #8 Repeat rate for left/right click, hold to continuously break/build

[satoshinm]

Depends on targeting the block being mined - continuously hit-test each mining tick, on_mine/build do these hit tests (first argument 0/1 = 'int previous'):

void on_mine() {

    int hw = hit_test(0, s->x, s->y, s->z, s->rx, s->ry, &hx, &hy, &hz);

void on_build() {

    int hw = hit_test(1, s->x, s->y, s->z, s->rx, s->ry, &hx, &hy, &hz);

Also retargeting should reset mining progress, to avoid mining wrong block quicker than it should