Add bigml histogram maven dependency
Add HistogramRollup class and test
Add HistogramSerializert class and test
Use stricter evaluation of histogram equals for tests
Address PR comments: fix cast, make variable public static final, fix histogram equals
Adding serialized histogram
Fix test to use MAX_BIN_SIZE
Merge pull request #97 from lakshmi-kannan/bf_add_histogram_support

RFR: Add histogram support (Round 1)