Allow specifiying multiple input directories

[kikugie]

This is useful when including optional resourcepacks in a mod.
getMoveOutputDirs is debatable whenever it should be a function or a map - would be glad to read your opinion on that.

[Fallen-Breath]

inputDirs sounds great.

For the moveOutputDirs option, I doubt if it's suitable to integrate such file management logic into yamlang itself. It doesn't seem to be what yamlang should do, since it's closely related to implementations of specific mods. You can just write some codes inside your gradle file and implement the moveOutputDirs yourself