Update 0.21 - Combat log and trade with travellers.

Clicking on potions in the villagers stats page will now instruct the villager to use it.
Added new combat log (keeps track of what monsters your villagers have fought with or tamed);
Added option to trade with travellers.
Reduced the brightness of white text.
Fixed issue where a sleeping villager could not be selected while the game was paused.
Fixed issue where monster info was not showing while game was paused.
Improved horse and mushroom towers sprites.
Minor bug fixes.
Some minor UI graphical improvements.