Improve sample source code

[bestchai]

Ideally, as samples, we would have different source code files for different kinds of instrumentations available (i.e., one per API). This will simplify the sample code, allow us to use filenames more descriptively, and will make it easier to find/index the relevant samples.

Also, each of the sample source code files in the repo needs annotations with information about exactly why each code block is there.