Config file support with bug fixes.

heapSpank now has its own config file -- heapSpank.properties.
You can tweak parameters in this file to slow down or speed up the frequency that jmap -histo is called.
To keep low overhead, by default, the jmap -histo -live option is not used -- it forces lots of extra GC cycles.
But, you can change this too, in the config file if necessary.

See the main page for details:

https://github.com/eostermueller/heapSpank

Details on all changes: #3, #9, #14.