Add two new options to CMakeLists.txt:

`BUILD_SHARED` - Whether or not to build the shared object (Default: ON)
`BUILD_STATIC` - Whether or not to build the static archive (Default: ON)

* Problem: Minor inconsistency in macro syntax. Solution: Code fixed.

Problem: FD set copying for Windows still not optimal in some places.

Problem: FD set copying on Windows still not optimal on some places. Solution: Improved memcpy() of FD sets for Windows builds.

Problem: Stack overflow in Windows VS 2012 builds for simple ZeroMQ u…

Problem: Stack overflow in Windows VS 2012 builds for simple ZeroMQ usage. Solution: Added notice in INSTALL file to mandatory use at least 2 MB stack size in VS 2012 and recommendation to use at least 2 MB in all other Windows builds.

RELICENSE: Pawel Kurdybacha grant

Fix compilation on windows using msys2

Problem: GCC 6 build fails due to misleading indentation and visually ambiguous if/else block ordering.

Solution: fixed indentation and if/else block.

RELICENSE: William Swanson

Critical BUG introduced with #2518 fixed.

Problem: Bad style in tcp.hpp/cpp

Solution: Add spaces between function
name and parentheses.

Another macro correction.

Consistency of Windows TCP tuning assertions

Treat ECONNRESET, ENETRESET and EINTR as non-fatal
failures in TCP Tuning on Windows as they are in the
Unixes.  Also adds ENETRESET to the Unix list that was missing.

Case found not covered in latest zmq::proxy() code.

Relicense: Tom Whittock grant

Reworked zmq::proxy() for improved performance.

adding licence

re-enable AI_V4MAPPED on FreeBSD & DragonFlyBSD

fix a typo - assigment was used instead of comparison

Detect AI_V4MAPPED is not supported in getaddrinfo() on the fly
and retry query. This issue was seen on ancient FreeBSD releases
and current implementation does support this flag correctly.

choose IP(v6) address based on ipv6_ flag in a correct way

* Relicense Grant - Thomas Rodgers (rodgert@twrodgers.com)