First draft of the new network combinators

That compile, but the implementation is full of TODO. The combinator signature should not change too much though.
Remove all the TODOs

Now need to check if the generated code is valid ...
Merge branch 'split-libs' of https://github.com/avsm/mirage into split-libs

Conflicts:
	lib_test/basic_stackv4/config.ml
Complete the port to the new network stack.

We now just miss the combinators for HTTP
Remove spaces
Port the tests to the new combinators

still need to port the HTTP test though
Merge pull request #1 from samoht/split-libs

Split libs