add support for speedscope

[sj-i]

See jlfwong/speedscope

Now you can use converter:speedscope to visualize traces via speedscope.
Both outputs from phpspy or php-profiler (the default phpspy-compatible format) are supported.

You can install speedscope on your local machine.

npm install -g speedscope

Then output traces from php-profiler

sudo php ./php-profiler inspector:trace -p <pid of the target process or thread> >traces

or from phpspy.

sudo phpspy -p <pid of the target process> >traces

Convert it to the speedscope format and open it by speedscope.

./php-profiler converter:speedscope <traces >profile.speedscope.json
speedscope profile.speedscope.json