DATAFU-49 Examples work again

* Removed dependency on Guava (which it didn't actually depend on) and on Piggybank (date functions are now first class)
* Path to datafu jar correct for current repo layout
* I made the quantile examples demonstrate a comparison of the exact vs approx algorithms
* Added the script to generate data for quantile.
* Quantile examples demonstrate both ways of constructing a Quantile UDF (number of partitions vs list of breakpoints)

https://issues.apache.org/jira/browse/DATAFU-49

Signed-off-by: Matthew Hayes <matthew.terence.hayes@gmail.com>
Update README files for examples

I wasn't able to run the sessionize script against pig 0.12.1.  It appears there is a bug in ToString that isn't fixed until 0.13.0.  Sessionize accepts ms time as the input in addition to iso time anyways though, so I removed this code that converted to an iso string.

I also updated the quantile's data generation script to output a file with a tsv extension.