fix a bug when (un)compressing sarray
move some utility functions to data/common.h
group_reader, which is a multi-thread reader, and can dump data into disk
group_reader in progress
passed group_reader_test
update localizer, but i'm going to refac instance.info now
instance -> example, group -> slot
passed slot_reader_test
passed localizer_test
update loaddata/preprocessdata in batchsolver, also delete cache/filter
in proper time
fix but in example_parser, can run on rcv1 and ctrc2 now
fix the bug that forgot to close the file
tested memory usage, servers are fine, but we may reduce workers' memory footprint
fix the bug that localizer do not release memory due to copy by value in
the lambda function