This commit introduces new socket_type enumeration values as well
as the following supporting functions:
socket_t::join()
socket_t::leave()
message_t::group()
message_t::set_group()
For header only library like cppzmq, whitespace style inherited from
libzmq is too restrictive.
Solution: relaxing whitespace before parens from always to in control
statements only, increased max column width from 80 to 85 and removing
requirement of whitespace after template keyword.
* Added overload constructor (c++11 only) taking iteratable object.
It would be easier to use std::string, std::array etc to construct
a message now. Making it a draft for now in case it is too greedy
and needs to be more specialize.
* Added equal and not euqal operator to message_t as a recommended
and expected way of comparing objects in C++.
* deprecated C style equal method as operator== should be used instead
(point above).
* Added message_t test covering all available message_t's constructors
