add getMongoClient to Fongo
refs #40 simple unique indexes
simple aggregator for min/max/last/first
 and  must handle null
clean import
add extractField on Util
Merge branch 'utilExtract' into minmax
add containsField on Util
Merge branch 'utilExtract' into minmax
use Util for containsField and get
simple rename for
more complex case in , need refactoring
Merge branch 'scalac16' into minmax
little refactoring
test sum of double
Instance + ThreadSafe
add
a little bit of group by
generalize test
Merge branch 'countskip' into minmax