add serial to json example

[twpayne]

This example is very similar to the existing stream-requests example, but emits JSON instead of log messages.

This example is particularly useful as a monitor when combined with a JSON tool like jq. For example, to display only heartbeat messages you can do:

$ go run ./examples/serial-to-json | jq 'select(.MessageType == "*minimal.MessageHeartbeat")

[codecov]

Codecov Report

Merging #80 (315224f) into main (f48820d) will decrease coverage by 2.78%.
Report is 33 commits behind head on main.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main      #80      +/-   ##
==========================================
- Coverage   83.76%   80.98%   -2.78%     
==========================================
  Files          24       26       +2     
  Lines        1786     2030     +244     
==========================================
+ Hits         1496     1644     +148     
- Misses        236      299      +63     
- Partials       54       87      +33     

see 17 files with indirect coverage changes

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[aler9]

Thanks for this example, it's particularly useful since this library currently lacks a storage format, and JSON may be a future storage format, along with binlog (bluenviron/mavp2p#24).

I'm not particularly happy about the fact that the standard JSON library can't handle NaNs, but i think it's a problem that can be handled in a second moment.

Please perform the following changes:

• add the example to the README
• replace log.Panic with panic since the latter is used in all other examples and it's the user responsibility to replace panic with his own error logic, without imposing usage of the log package.

[twpayne]

Thanks for the review. PR updated.

I'm not particularly happy about the fact that the standard JSON library can't handle NaNs, but i think it's a problem that can be handled in a second moment.

It's not the standard library which is at fault here: JSON has no way of representing NaNs, indeed there is no string format for NaNs that I know of.