Support "relative" Window positions and sizes.

[tmontes]

Not sure if it should be handled by the kernel of the lib... (maybe the kernel as it may simplify handling automatic output terminal resizes).

Ideas:

• Position
  • Defined by two args: x and y.
  • Positive int values correspond to zero-based, absolute terminal coordinates.
  • Negative int values correspond to "from-right/bottom" absolute terminal coordinates, where -1 corresponds to the last "column/row".
  • Positive float values correspond to zero-based, relative terminal coordinates where 1.0 is the first "column/row" after the visible ones.
  • Negative float values correspond to "from-right/bottom" relative terminal coordinates, where -1.0 is the first "column/row" before the visible ones.
• Size:
  • Defined by two arguments: w and h.
  • int values correspond to absolute terminal "rows/columns".
  • float values correspond to sizes relative to the terminal geometry with 1.0 represents the full width/height of the terminal.

May be of use:

• Some kind of dx, dy, dw and dh to somehow manage margins.

Examples:

• A full-screen window: w = Window(x=0, y=0, w=1.0, h=1.0).
• A full-screen window with a 1 row/column margin: w = Window(x=0, y=0, w=1.0, h=1.0, dx=1, dy=1, dw=-2, dh=-2)
• Two side by side windows: w1, w2 = Window(x=0, y=0, w=0.5, h=1.0), Window(x=0.5, y=0, w=0.5, h=1.0) (may need dx/dw adjustments to ensure there is no overlap?)

That's the general idea.

[tmontes]

After PR #87 and #88, this is completed. Closing.