add config file

[benfred]

It would be pretty great to have a persistent config file, with the main initial use case being the ability to exclude certain functions (mark them as idle for the purposes of sampling).

[earonesty]

yeah, this is a pretty serious/annoying thing when profiling programs that use lots of threads, queues, and ipc calls. you wind up with 99% of your time in poll() select() and other blocking calls that are intentionally idle

this helped for some stuff, but not all. 3ef940a