One side effect of the way that Go's flag library works is that any
flag that's defined at the global scope by any library that's built
into your binary shows up in your help -- whether you honor it or
not. Arguably, including the library and calling its entry points
should be tantamount to honoring the flags. This change makes the
profiling flags behave that way -- there's one function that you call
to turn on whichever kinds of profiling the user specifies on the
command line. It returns an object with a Stop() method that you call
to shut down profiling and flush data, like so:
defer profile.MaybeStartProfile().Stop()
