Add helper function for change_ methods

[olsonk]

Code often checks whether the given change amounts would set the attribute beyond the max/min values. Create a helper function that can check for this situation and modify the attribute accordingly.

[olsonk]

Added helper function that guarantees that requested "change" amounts are within allowable limits. Function provides useful feedback when outside of allowable bounds - requested value, max/min allowed, and what it is being set to. See this commit.