RF: Have attributes width and height aliased with size in RectStim.

[mdcutone]

Fixes issue #2644 by aliasing width and height with size.

Behavior of __init__ has been changed to use size only to set the dimensions of the rectangle. Keyword arguments width and height set size. If size is specified, the values of width and height are ignored. Documentation has been updated to reveal this new behavior. Attributes width and height can be set after initialization so operations may be used to manipulate the shape of the rectangle in one dimension. Changing the size attribute will also update the values of width and height.

[lgtm-com]

This pull request fixes 2 alerts when merging b7c14a2 into 8db8521 - view on LGTM.com

fixed alerts:

• 1 for Unused import
• 1 for Module is imported with 'import' and 'import from'

[lgtm-com]

This pull request fixes 2 alerts when merging 9830151 into 8db8521 - view on LGTM.com

fixed alerts:

• 1 for Unused import
• 1 for Module is imported with 'import' and 'import from'