blocking way. The channel code is now responsible for enabling/disabling
blocking status and to work with it.
I've also modified indenting and fixed compiler warnings at places, and
added a bunch of new examples in example/simple that I've used to verify that
the code still runs like before.
libssh2_channel_{read|write}nb_ex() and libssh2_sftp_{read|write}nb() are the
four new functions that supposedly work non-blocking.
