Add basic socket support (#428)

* Add a descriptor class for socket(2) return values

* Add basic socket(2) and bind(2)

* Basic accept(2)

* Basic recv(2) support

* Debug statements and accept(2)

* Add check for symbolic arg to open(2)

* Fix an example warning

* send/sendfile

* debug->info for some mcore output

* Produce socket data as part of state serialization

* Clean up SLinux.sys_open()

* Document socket(2) peculiarities

examples/linux/basic.c

@@ -35,6 +35,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <unistd.h>
 
 int main(int argc, char* argv[], char* envp[]){
     unsigned int cmd;