VarType: made var_type_name() inline.
VarTemplate: made VarMask ctor non-explicit.¹

1: Too tedious when making initializer lists.
EncodingUtils: removed pointless cast in UTF8Utils::decode().
VarUtils: corrected convert_typed() for sign-only or decimal-only strings.¹

1: '.' or '-' or '+' were considered numerics because the presense of
numerals was not being considered.