Release v4

Makefile: Add support for new interface- and hopperboards

- This adds interfaceboard v1.5 to the list (again). Which is probably forgotten
during the previous makefile overhaul.
- Add interfaceboard v1.6.
- Add hopperboard v2.0 and 2.1

Release v3

Add support for Interfaceboard v1.5

Bootloader: Put bootloader name and version in hex filename

BootloaderTest: Remove ackLastRead

Turns out that acking the last read is actually problematic for the I²C
protocol, since then the slave does not know the transfer is completed
and might pull SDA down. This prevents the master from sending a stop
condition. In practice, this did not happen because the slave politely
withdraws from the bus when its last databyte is sent, but it is not
required to do so.