errors: switched to pure Go error implementation, not just error code
errors: operate on error pointer like described in golang tour
Merge branch '1.3' of github.com:noxiouz/elliptics-go
session: added more setters: ioflags, cflags, trace id
session: switched read/write functions to work with []byte instead of string and get rid of unused copies
write: fixed _ = data typo
Merge pull request #8 from bioothod/master

2.25 sync: added error class, session flags and use []byte as argument instead of string