Merge changes from PR #47 related to windows platform support.
Add full windows platform support including correct error checking and working regression tests and examples.
Remove need to build applications using libcoap with -DWITH_POSIX and to include coap_config.h. This applies to the examples as well.
The testdriver was linked against the statically generated library of
libcoap. By this the testdriver will *always* find any symbols, no
matter if it is a private or public symbol.
Due this the testing behavior isn't the same as a user would use the
shared library and can get a potentially pitfall even if the testdriver
was successful.
Due previous changes to the public header the testdriver source needs
now the local header coap_config.h to find all needed functions so there
are small changes needed to the source files.
The subdirectory "tests" now contains a growing set of unit tests for the
libcoap API. To use this, you will need CUnit (see http://cunit.sourceforge.net)
and must configure with the option --with-tests.