This macro looks at each cell along some stride through the sheet,
returning the location of the first cell encountered at which a given
expression evaluates to true, or boolean false otherwise.
To make this more useful, this change also revamps the handling of
boolean values, making them much more permissive and coercing to boolean type
in fewer circumstances. It adds the bool() type conversion for explicitly
coercing to boolean type, and fixes a small issue with reading hex-formatted
floating-point values ('p' can be used as an exponent indicator).
Closes#64.
06938ec494