Adding support for unit tests on windows systems

This pull request adds support for unit-testing on windows systems, without installing any addons like cygwin or other workarounds for windows.

__modified:   Readme.md__
* Added the section 'Running unit tests on windows'

__new file:   make.bat__
* On windows systems there is normally no 'make', so this patch adds a make.bat with environment variables to be edit by the user. It will be found by npm or can be execute from cmd-line. The pull request assumes, that the file 'make.bat' is not executed on unix. 'make.bat' contains the environment variables queried in ```test/common.js```.

__modified:   test/integration/connection/test-unix-domain-socket.js__
* Modified since there are no unix-sockets on windows systems, I guess. 
The script now checks, if the environment variable ```windir``` is set. If it is set, it will skip the two tests and invert the assertion. The script assumes, that the environment variable ```windir``` is not set on unix systems.