Add -M option for machine-readable JSON output

[bstee615]

This PR adds the -M short option which converts the output of ts or ts -l to JSON.
Also, I enabled CUDA build for an older CMake version (3.16) which is the latest by default in Ubuntu's package manager.

I implemented it with cJSON, which I added directly into the project. It is compatible with ANSI C so should not restrict any platforms.
I added a test to testbench.sh, not sure if any other test suite exists.

Please let me know if there are any other requirements for implementing this feature.

Example:

~/code/task-spooler-structured-output/build-gpu master*
❯ ./ts -K

~/code/task-spooler-structured-output/build-gpu master*
❯ ./ts echo foo
0

~/code/task-spooler-structured-output/build-gpu master*
❯ ./ts sleep 10s
1

~/code/task-spooler-structured-output/build-gpu master*
❯ ./ts
ID   State      Output               E-Level  Time   GPUs  Command [run=1/1]
1    running    /tmp/ts-out.vj9wHU                   0     sleep 10s
0    finished   /tmp/ts-out.tFVNpx   0         0.00s 0     echo foo

~/code/task-spooler-structured-output/build-gpu master*
❯ ./ts -M json
[{"ID":1,"State":"running","Output":"/tmp/ts-out.vj9wHU","E-Level":null,"Time_ms":null,"GPUs":0,"Command":"sleep 10s"},{"ID":0,"State":"finished","Output":"/tmp/ts-out.tFVNpx","E-Level":0,"Time_ms":0.0018889999482780695,"GPUs":0,"Command":"echo foo"}]

[bstee615]

By the way, could you add the hacktoberfest-accepted label to the PR if it is accepted so I can get credit for hacktoberfest? smile

[bstee615]

Implements #25

[justanhduc]

Hey @bstee615. Thanks a lot for your effort! This week I am quite occupied to prepare for my defense, so I will review soon within next week.
Btw, why -M while both -j and -J are available and seem to be a more natural choice?

By the way, could you add the hacktoberfest-accepted label to the PR if it is accepted so I can get credit for hacktoberfest? smile

Of course! Let me figure it out how to use it first.
Again, thank you for the PR.

[bstee615]

No problem about the time line, good luck on your defense.
I chose -M for "machine-readable", where the user can give options other than JSON. Currently tsp -M json gives JSON output, maybe later we would want to add tsp -M csv. I have no strong preference on that, so I can change it to a binary flag -J if you think it's better.

[justanhduc]

Hey @bstee615. Before merging, I would like to double check. Is the hacktoberfest label valid?

[bstee615]

Yes, the label is valid. Thanks for the review!

[justanhduc]

Thanks a lot for the PR @bstee615. Please let me know when the GUI is usable!