Add div family methods (div, cld, fld, rem, mod)

[BioTurboNick]

This PR adds the div family methods (div, cld, fld, rem, mod) and operators (÷, %) to the set.

Since integer division is so slow (see #9), we can afford branches to avoid undefined behavior produced by just using the intrinsic directly. Could consider an unsafe mode, but unclear benefits from that at this stage.

For unchecked methods, we're defining divide-by-zero to produce zero, and typemin() ÷ -1 to overflow to typemin(Int).

For saturating methods, we're defining divide-by-zero to produce typemin(), zero() or typemax() based on the sign of the dividend, and typemin() ÷ -1 produces typemax().

Base.divrem isn't present at the moment because Base.Checked doesn't have a checked_divrem method. Also, Base has a complicated infrastructure for rounding modes that isn't implemented here because Base.Checked doesn't either.

[BioTurboNick]

Tests still need to be made more complete.

[BioTurboNick]

Since this substantially changes the behavior of what happens inside the macros, this will also be 0.3.