Kernel/LibC: Implement basic epoll

This implementation is on top of inodes instead of fds as linux does it.
If I start finding ports/software that relies on epoll allowing
duplicate inodes, I will do what linux does.

I'm probably missing multiple epoll_notify's which may cause hangs but
the system seems to work fine :dd:

userspace/libraries/LibC/CMakeLists.txt

@@ -30,6 +30,7 @@ set(LIBC_SOURCES
 	string.cpp
 	strings.cpp
 	sys/banan-os.cpp
+	sys/epoll.cpp
 	sys/ioctl.cpp
 	sys/mman.cpp
 	sys/resource.cpp