Rename `{import,export}Integer`

This renames to more verbose names which include the type these
operations import/export from/to:

 - `importIntegerFromByteArray`, and
 - `exportIntegerToMutableByteArray`.

This follows the naming convention used for other primitive operations,
such as the recently added `copyMutableByteArrayToAddr` operation.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
Add `Addr#` based `{import,export}Integer` variants

These follow closely the existing implementations for
`importIntegerFromByteArray` and `exportIntegerToMutableByteArray`.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
Optimize order of pattern matches for export operations

These are supposed to be called with `J#`-kind `Integer`s, so check that
constructor first.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
Improve Haddock documentation

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>