fl for from_left and fr for from_right, but nothing between

[GantMan]

Frame settings of left and right can sometimes be thought of as from_leftbut fl will silently fail.

This issue is 2 fold:

• First, add our friendly aliases for fl
• Second, stop being silent and throw a warning when we get strange frame demands

The check for strange frame keys should be extremely performant

[GantMan]

@twerth says this should throw a warning, not an exception. Original edited.