Present profiles nicely

[mo-mglover]

Several bits:

• At the moment, a separate profile appears for each thread. Instead, only present a single profile with thread max/min info.
• Write to a suitable output file.
• Sort the profile entries in order of decreasing self time; perhaps optionally the total time (inclusive of child routine calls).

[andrewcoughtrie]

Is it worth/possible to include something like a grouping option? it would probably require some sort of namespacing with the calipers but would be useful.