new collector options, new file collector, and minor doc update

Minor updates/additions/fixed for Diamond

1) doc Update in Example.py.  Simpler way for testing a module, especially those that require run over run multiple gathering of metrics

2) New FilesCollector that will collect metrics from file(s) in a special pickup directory
options:
   'dir':     'The directory that the performance files are in'. Default /tmp/diamond
   'delete':  'Delete files after they are picked up', Default False
   'path':    'additional prefix added to metrics collected'.  Default '.' (don't add a prefix)
File format is just lines of 
  metricname.metricname.whatever:10.2
  another.value:12345

3) Update to CPUCollector, new option 'normalize' (default false).  When set to true, 'total' cpu metrics are divided by the number of cores (so that total is always 0-100%)

4) Update to DiskUsageCollector, new option 'send_zero' (default false).  When set to true, metrics are still sent to graphite even if there was no IO during the previous period

5) Update to DiskSpaceCollector, new metrics for _percentfree and inodes_percentfree
For testing collectors, create a directory (example below for /tmp/diamond) containing your new collector(s), their .conf files, and a copy of diamond.conf with the following options in diamond.conf: