Add binary I/O to the SHA types.

[myrkraverk]

I made an implementation of binary I/O for the various SHA types.

For now, I'm not making it a pull request because my work depends on the Windows port, which is already a pull request.

I bumped the version to 0.1.6 and made an upgrade script based on help from the PostgreSQL General mailing list.

I did not touch the .in files, and copied hashtypes--0.1.5.sql directly. I did not touch sha.sql.type because I don't know how it's used to generate the install script.