stat: added dstat stats (disk util and read/write per second performance)
stat: export pure structure into json, without need to convert its field into interfaces
session: added filters and write/lookup error parsing
stat: do not convert utilization into percents, use raw data (without 100 multiplication)
stat: added defrag state, ro/delay and blob size limit
addr: added DnetAddr-from-string helper
backend: added backend control helpers: enable, disable, start defragmentation, set delay, make read-only and writable and read status
addr: we must use slice in DnetAddr, since len(addr) must correspond to the actual address length. But for map indexing we need a fixed-length structure, so introduce RawAddr with array instead of slice to hold address content
backend: implemeneted backend status reply parsing
vfs: move total size limit into VFS section
addr: use new address-to-string conversion C functions
addr: fixed remote nodes array insertion
stat: fixed RawAddr.String() method, it must use correct address length, by default it used array size, which is too big and can not be used to determine socket type
session: added server+backend lookup method which uses local route table to locate needed pair for given key and group
stat: added pid regilator and FindStatBackend() helper
error: added method to convert generic error into DnetError
stat: when doing diff between previous and current stats, copy PID data from old to the new structure
stat: added backend error structure, only 'code' field is supported and used
addr: added DnetAddr() method to RawAddr pointer type, it constructs DnetAddr pointer from RawAddr pointer
stat: get rid of interface{} stat API, use structures instead. Propagate number of records into VFS stats.