implement else macro

[amoibos]

This would be nice and shouldn't be that hard.

[haroldo-ok]

I agree, though it would also require the implementation of an 'else' instruction on the SAM interpreter.

[amoibos]

My suggestion add a | symbol for the else branch within block. The start depending now of the expression. If it true skip all commands between | and ] otherwise ignoring all between [ and |. On my branch i already added the changes for the parser.