Proposed radiation handling

[aerkiaga]

As stated in #7 and discussed with @forked-from-1kasper, I am contributing some changes to the way radiation is handled. This includes:

• Ray-casting so radiation through walls is handled correctly (slow for polluted mercury oceans, fast elsewhere).
• Updated activity values using the actual experimental activities when possible.
• Different attenuation for each material so walls can screen radiation to a different degree.
• Different ionizing power for each type of radiation.
• Doses in Gy, with an approximate conversion from activities that at least appears reasonable.
• Updated thresholds for each radiation effect, and a weakness effect.

Effects:

• It's easier to find shelter from radiation, as the ground tends to screen all radioactive ores below.
• Plants and uranium are not much more or less dangerous than before this PR.
• Thorium is almost non-radioactive.
• Americium and plutonium are so radioactive that coming anywhere near their ores would yield a lethal dose of radiation instantly. To prevent this, I've capped the maximum amount of radiation to 1 kGy/h, but a player would be forced to avoid them anyway. Some mechanism is required to allow crafting with them.

[aerkiaga]

OK, the idea is that now radiation is more of a discrete hazard that can and must be avoided. Strong sources of radiation can kill the player in under 15 seconds, so it becomes necessary to be careful and check if the radiation counter becomes unusually high (could be made easier with some sort of sound effect, maybe a classic Geiger counter sound?). It is also easy to shield oneself from them by placing any block in the way. Finally, players could effectively "cure" radiation now using anti-radiation drugs, which allows them to turn radiation into a material, rather than existential threat, if they are able to craft the drugs.

It remains the question of how the player would become able to handle plutonium and americium ores. They are not very useful at the moment, so that is not a concern right now; however, it now becomes necessary to provide players with ways to pick up, store and craft them, e.g. an improved space suit with anti-beta inventory (thus immune to plutonium).