session: added parallel lookup method
elliptics: initial v2.26 implementation
log: elliptics node writes its log intormation into standard Go log.Logger now
session: implemented prepare/write/commit methods, use io.Reader in upload

These methods are used for large file upload - we prepare enough
space on disk, put multiple chunks into the file and then
commit desired size. Default chunk size is 10m, files less than that
are read into memory and uploaded via common write_data() method.
Reading from io.Reader can return less than maximum chunk size,
we start writing data into elliptics as soon as there is something.

Since upload methods are now using io.Reader they do not buffer
too many data, at most chunk side per goroutine.

Returned channel yet contains a mess of combined json objects each
per written chunk, this will be cleaned next.
chunk-write: only put the last write result, i.e. the one after commit message, it contains correct information
session: switched to uint64_t instead of size_t. Added offset/size read/write parameters.
session: added GetGroup(), store groups in local session. Added chunked read and streaming read interface, which streams data into http pipe
node: extended default logger format
node: increase default number of io/net node's threads. Fixed blackhole log formatter.
node: fixed node creation check, return error if not could not be created
stream: only set size to total_size if client set it to 0
stream: if requested size is more than file size, set it to file size
stream: set correct content length based on actual size to read and not file size
dnet_cmd: all members of the packed structures must be accessed via special getters()
keys: added keys array structure. It sorts provided data and allows to find key. Used by BulkRemove() operations
remove: remove callback returns command now
session: remove callback returns cmd,key,error structure. added BulkRemove() method.
addr: made DnetAddr structure on top of array not slice to allow it to be part of the map key. Added DnetRawID type.
route: added route tablereading classes and methods
stat: added initial global statistics implentation