Book update for firmware 1.9, software update 1.2.6856

The book was updated for the upcoming release 1.9 of the firmware for the Black Magic Probe.
The archives for the binaries also contains the PDF for the book.

Firmware 1.9 no longer sends a handshake on toggling DTR, like releases 1.8 and before did. The utilities that talked to the BMP directly (via GDB-RSP), depended on this handshake, and therefore no longer worked. This release fixes this.

All GUI utilities now have integrated help. Also added is that the GUI utilities monitor USB insertion & removal events, so that they can detect that you plug in a BMP while the program was already running (or that you remove the BMP while the program is still running).

A serial monitor/terminal was added to the set of utilities, not just because the BMP happens to have a TTL-level UART, but also because the BMP translates RTT to serial, and optionally translates SWO tracing to serial.

The "blackmagic-hosted_Win32.zip" file is the "Black Magic Hosted" firmware software from the blackmagic project, built for Windows. This application is also known as BMA (Black Magic App) or BMPA. It is useful for troubleshooting, but not otherwisely needed to use the Black Magic Probe or the software. The executable version of this utility for Windows is available here only for convenience.

The "cflow_Win32.zip" is the GNU cflow utility, pre-compiled for Microsoft Windows. It is available here only for convenience.