fixing logic error in keyword indexing max --> min on the term
frequency to keep it under 255.
Creating a simple profiling utility for the keyword bit packing stage:

2014-11-08 19:43:17,704 pid=18320 test_keyword:88   INFO     running with /data/kbp/2009/kbp2009-serif-basis.sc.xz
2014-11-08 19:44:09,306 pid=18320 _kvlayer_key:57   WARNING  no so.body.clean_visible on 1395343209-e78ee6dae437ac284eb6443f3a8ef9c9
2014-11-08 19:44:10,866 pid=18320 test_keyword:72   INFO     3688 SIs, 12.7 clean_visible MB, 692448 tokens, 1.3 index MB in 5 seconds --> 723.9 SI/sec, 2.5 MB/sec, 135923.8 tokens/sec, 0.3 index MB/sec

This example illustrates how 12.7 MB of text --> 1.3 MB of bit-packed
tokens for indexing.  That savings is the result of stopword
filtering, trimming to counts, and struct.pack