Flag to encode system timestamp in Beast output

[xander-hirsch]

The --beast-sys-time flag allows a user to specify that Beast output messages should include the system timestamp (in milliseconds since the epoch) instead of an input device-specific timestamp. Providing this flag does not change the timestamp printed with each decoded message such as the example in issue #163.

[mutability]

What's the expected use of this new format?

Have you considered using the Radarcape-style timestamp format (which represents nanoseconds since UTC midnight) rather than introducing a third format?

I think this would need to be controlled by a negotiated option to avoid confusing existing software.

[xander-hirsch]

I've revised this pull request to incorporate your suggestion of a Beast client negotiated option, enabled by "<esc>1T".

My motivation to provide system timestamps is to enable a much simpler record/replay solution. For example, a user can run $ printf '\x1a\x31\x54' | nc localhost 30005 > capture.bin to record messages for a particular duration and replay them with timing information.

I considered the Radarcape-style timestamp format; however, the date information is needed for the aforementioned use case.