Bugfixes and tests.

Bugfixes:
 - Node.AddRemotes: returns error in case of an empty array of remotes

Test coverage: 14%
Enhancement of API. Export DNET_IO_FLAGS and DNET_FLAGS

Enhancement:
 + Added getters for Cflags, IOflags, Timeout, TraceID
 + Set/GetTraceID, Set/GetIOflags, Set/GetCflags accept a custom type
 instead of uint32_t/uint64_t
 + cflags, ioflags are hidden under typedefs

Testcoverage:
 + 15%