Currently the fields is a list of lists of strings. This will needlessly
consume RAM so lets switch it over to a simple string (which is immutable
and can be stored in flash).
We also replace indices with simple x and y variables. In addition to
avoiding a (temporary) memory allocation this is also easier to use
when looking up in fields.
Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>
Currently the calculator uses an open grid. It's a matter of taste but
I prefer a closed grid.
Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>
Currently the coordindates used for line drawing are "tuned" for a bug in
the line drawing code (and now draw off the edge of the screen). Fix this.
Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>
