Import profiler.enable documentation from xhgui project

[glensc]

refs:

• Update documentation xhgui#293

[glensc]

I'm thinking of having 'profiler.enable' also to accept boolean true/false values for simplicity. and having default value to be true.

@markstory wdyt?

[Krinkle]

Perhaps the non-function value could be an integer rather than boolean, e.g. for population size (enable=1 is on, enable=0 is off, enable=100 is 1:100 sampled); or a float for sample rate (e.g. enable=0.01 is 1/100).

Having said that, I'm also all for minimalism and letting the caller own and provide the sampling method. So perhaps that's unnecessary.

[glensc]

@Krinkle seems un-necessary to put the logic to library. people start to complain if it doesn't work right :) I would say that using rand is not pedantically accurate, to get exactly 10% of users you need to count them, which means the need for a shared database, and perhaps even locking :D

however, I do see value having simple "off" (0%) and "on" (100%) use.