Doc for module Clock (UNIX/Xen)
Documentation for module Time (UNIX/Xen)
Documented module Start_info (Xen)
Added doc for module Env (UNIX/Xen)
[doc] Titles and typos.
Merge pull request #42 from vbmithr/doc

Doc
[doc] Documentation for module Sched (Xen)
Improved function Netif.create for the Xen backend. Now the cleaning code should be called on failure
Unifying modules Netif across the UNIX and the Xen backend
Normalized the doc of the Netif interface for the unix backend
Export the type Netif.id as being a string