Test length when making a Slct

Implement APL-like printOn()

Implement type conversions

Eliminate glueball

TYPESlice::TYPESlice(const TYPEPick&) and
TYPESlice::TYPESlice(const TYPESlct&) should be implemented as
TYPEPick::operator TYPESlice() and TYPESlct::operator TYPESlice(), but
this currently doesn't work because TempTYPEVec get destroyed on return.