Separate the bigint, bignum, and bigrat pragmas. The bigint pragma now converts every numeric constant that represents an integer to a Math::BigInt object. Non-integers are converted to Math::BigInt NaNs. With the previous behaviour, only some numeric constant integers were converted to a Math::BigInt. The bignum pragma now converts every numeric constant to a Math::BigFloat object. The bigrat pragma now converts every numeric constant to a Math::BigRat pragma. The pragmas no longer activate upgrading and downgrading. The upgrading and downgrading must now be activated explicitly. The rationale behind deactivating it by default is that can cause infinite looping where objects bounce back and forth between different classes. Explicitly requesting a specific class doesn't always work either, because the object might be automatically upgraded or downgraded to a different class. Only one pragma can be used at a time in a given scope. Enabling one pragma disables the others in the same scope. Implementat working version of "no bigint", "no bignum", and "no bigrat". Previously, the upgrading and downgrading activated by, e.g., "use bigint" was not deactivated by "no bigint". Sync behaviour with the Math-BigInt distribution.