Fix up building czmq as a DLL

 * If czmq is a DLL, set CZMQ_EXPORT to declspec(dllexport) when building czmq,
   and declspec(dllimport) when building against the czmq DLL.  Unset
   CZMQ_EXPORT otherwise
 * Make sure to link against the appropriate multi-threaded DLL runtime when
   building czmq as a DLL.
 * Put the libzmq directory into "Additional Library Directories" instead
   of putting the path into the "Additional Dependencies" field
 * Make sure the czmq library path is in for the czmq_selftest project
Fix up czmq_selftest builds on Windows in DLL mode

 * Export all the *_test() functions
 * Cleanup the library location for czmq (and remove the libzmq and other libs
   - the czmq library will pull them in)
Remove stray include file from czmq.vcproj

stdbool_for_windows.h was never used
Merge pull request #134 from vortechs2000/fix_windows_dll

Fix windows dll builds - Fixes issue #132, and issue discussed in issue/pull request #133