Added the unique skill "Covert"

The unique skill "Covert" has been added to Lara. Holders of this skill double the avoidance effect of terrain.

This was inspired by the class characteristics of thieves in Engage. In this hack, the formula of Avoid is changed to be lower, so there are many situations where it is difficult to have a quick unit act as an avoid tank, but with this skill, it may be possible to act as.

If the terrain effect (avoidance) is negative, the value is not doubled.