ds1054z v0.4.0

This release is upgrading the software for use with the latest firmware and introduces some new features and speedup.

Bugs fixed:

• ds1054z save-screen <hostname> now works again with the latest firmware versions. (Maybe it doesn't work anymore with older versions! I highly recommend upgrading to 00.04.04.SP3 (alias 00.04.04.03.02).)

Improved speed:

• The ds1054z save-screen <hostname> is now many times faster than before. This is due to the fact that the PNG format is used to download the screenshot from the oscilloscope, which is just ~4% of the size of the previously used BMP24.

New features:

• Small unittest tests/test_communication.py (well, sort of). It needs the oscilloscope itself to do the checks including the I/O. The test coverage is not very broad yet and it's not automatically run so far. But it's a start. If you want to run it, do ./tests/test_communication.py <hostname>.
• DS1054Z.memory_depth property
• DS1054Z.display_channel() method
• DS1054Z.display_only_channel() method

Code-wise, the differences to v0.3.8 can be checked here.