rename Type::Tiny::HalfOp to Type::Tiny::_HalfOp

--HG--
rename : lib/Type/Tiny/HalfOp.pm => lib/Type/Tiny/_HalfOp.pm
rename : t/overload-precedence.t => t/20-unit/Type-Tiny-_HalfOp/overload-precedence.t
be a bit more ambitious with syntax.t