Cache: concurrent_time_tree, erase from page, time_tree difference

- Concurrent time tree added to handle concurrent updates
- Erase from page optimization added to avoid iterating removed records
- Methods to find time stats trees difference added
Cache: Append optimization added
Cache: syncing to disk during requests to cache removed
Cache: fixed size stats counting for deleting objects
Monitor: json allocator for dynamic string added
Uninitialized fields shown by valgrind fixed
Core: Limited size of io queues to the number of io threads * 1000. Added building iterate.cpp from example to main build without installation.
cpp: Changed mix_states behaviour

Now it don't throw exception but returnes non-positive error_info
object to determine if mix_states was successfull
WIP: Documentation warnings
Added forgotten doc/Doxy*.in files
Get rid of get_node calls
docs: Don't try to install documentation

Debuild/rpm scripts are not ready for it yet
tests: Don't make artifacts if test is successfull
Cache: time_stats docs clarified
Tests: Order of cleaning after testing changed.

Now we remove test directories in the very end.
Cache: Resize page optimization.

Record is pre-cleaned from page before actual eviction. This way we
don't iterate twice over records that were evicted but are still in page,
waiting for sync.
Cache: Elements that were removed while being in sync queue don't sync now.
Core: added checking epoll_events
Merge pull request #343 from euroelessar/master

Doxygen & mix_states improvements (master)
pool: added comment on how client handles replies in multiple IO threads
Core: removed useless checks.
Monitoring: Added rwlock on access to dnet_node::monitor