Correct gsl to generate Makemodule.am instead of Makefile.am.supplement.  Move src/Makefile.am to src/Makefile
Restore 'doc' to recursive make, matching libzmq.
Revert experimental make root invocation.
Fix break introduced by #768.
Merge pull request #771 from pmienk/master

Correct doc generation, restore make target results into previous structure.