Scalar: set # of active bits to 21 (default), forced to override

you can use any number, if you provide forced=True to the constructor
pass forced=False parameter to each encoder using ScalarEncoder
add forced param to AdaptiveScalarEncoder
add forced param to delta encoder
add forced to logenc
add forced param to nonuniformenc
forced param for scalarspace
examples use forced=True (! not recommended)

just used for compatibility and readability. All new real applications
are advised to keep forced unset and obey the check w>=21 ON bits