new I/O multiplexer api; http echo server example draft to test the mux api; the library is now released as an amalgamation; recv/send now return the error MICROTCP_ERRCODE_WOULDBLOCK in a similar way to the BSD socket api; moved tests/loop2.c to examples/echo_tcp.c

src/icmp.h

@@ -1,5 +1,8 @@
 #include <stddef.h>
+
+#ifndef MICROTCP_AMALGAMATION
 #include "defs.h"
+#endif
 
 typedef struct {
     void  *output_ptr;