Expose the upgrades of enemy units

Hi,

After seeing the new visual indicators of unit specific upgrades (very nice) I was reminded that this information is not available for enemy units via the api. First and foremost, a human just needs to select an enemy unit and the upgrade level of said unit can be seen. This can influence the decision whether it is time to attack or retreat. Moreover, in specific situation, for example whenever it is Phoenix vs other air unit, it is quite important to know whether the enemy Phoenix have the range upgrade or not.

At the moment one can get the upgrades of oneself via getUpgrades. But it does not make sense to make the information of enemy units always available. To stick with the example, you have to see a Phoenix once after the researched finished to know that it has the upgrade.

This is why I propose to put the [buffs](https://github.com/Blizzard/s2client-api/blob/e7346e441e3ccdc321607d4ed1e200287945cc01/include/sc2api/sc2_unit.h#L186) field to be available to both players (I don't see a buff that is hidden in the real game/ shouldn't be revealed when you have vision of said unit). Then add the unit specific upgrades as buffs. For example, if my opponent has stim, 1+ infantry weapons, and concussive shells, then a marine should have stim and +1 in the buffs, a marauder should show all three and a worker none. The values will not be updated when the unit is not visible, of course.