Add corresponding MIN_* values for MAX combat values

Closes #552

This includes supporting minimum values for:
* absorb
* block
* elemental resistance
* avoidance
Added hp/mp ratio preservation logic for effects that change maxhp/mp
Merge pull request #630 from dorkster/min_combat

Add corresponding MIN_* values for MAX combat values
Fix activating passive hero powers that have no requirements

Fixes #632
Codingstyle: Use the wiki entry, add examples, talk about brackets
Merge pull request #619 from stefanbeller/codingstyle

Codingstyle: Use the wiki entry, add examples, talk about brackets
Merge remote-tracking branch 'upstream/master'
Fix init order warning in StatBlock
Merge pull request #1 from dorkster/ratio

Fix init order warning in StatBlock
Merge pull request #641 from blazindragon/master

Bonus HP/MP Effects Preserve Ratio
Merge pull request #636 from dorkster/passive_powers

Fix activating passive hero powers that have no requirements