Lib gui box

[TDW89]

closes #59 tested everything working. does increase inter-dependency for some lib_menu and lib_number_dialog also in sanitizing the inputs I have made the bottom line unusable (as using the bottom right corner causes all the on screen text to shift) it was that or block the right hand edge.

I have also changed the default box from:

+=====+
|     |
|     |
+=====+

to:

+-----+
|     |
|     |
+-----+

This was mostly done out of personal preference for having the horizontal and vertical line styles match in the default box.

[TDW89]

also addresses issue #51

[TDW89]

@space-is-hard could you give this a quick look when you get the chance. Thanks

[space-is-hard]

Looks good. Merging.