The keyboard now only allows up to 6 digits of precision

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
Symbol will now round to 6 decimal digits, fixes #92

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
MathView now only allows a single variable as input for the 'integrate over' child.
Fixes #78

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>