Update for the docs/api-client-libraries.md file.
Update for the docs/api-client-libraries.md file.

Added Operator API section, and added mesos-operator-api-client to
that.

This closes #219

kaysoky/mesos,chhsia0/mesos,neilconway/mesos,Gilbert88/mesos,asamerh4/mesos,kaysoky/mesos,reneploetz/mesos,chhsia0/mesos,kaysoky/mesos,andschwa/mesos,verizonlabs/mesos,abudnik/mesos,zmalik/mesos,asamerh4/mesos,kaysoky/mesos,dforsyth/mesos,neilconway/mesos,kaysoky/mesos,gsantovena/mesos,jpeach/mesos,chhsia0/mesos,jpeach/mesos,verizonlabs/mesos,neilconway/mesos,abudnik/mesos,jpeach/mesos,asamerh4/mesos,abudnik/mesos,asamerh4/mesos,dforsyth/mesos,andschwa/mesos,reneploetz/mesos,Gilbert88/mesos,reneploetz/mesos,jpeach/mesos,verizonlabs/mesos,neilconway/mesos,dforsyth/mesos,kaysoky/mesos,Gilbert88/mesos,zmalik/mesos,Gilbert88/mesos,gsantovena/mesos,chhsia0/mesos,andschwa/mesos,reneploetz/mesos,gsantovena/mesos,andschwa/mesos,gsantovena/mesos,jpeach/mesos,jpeach/mesos,reneploetz/mesos,Gilbert88/mesos,zmalik/mesos,zmalik/mesos,Gilbert88/mesos,neilconway/mesos,chhsia0/mesos,asamerh4/mesos,gsantovena/mesos,asamerh4/mesos,neilconway/mesos,reneploetz/mesos,reneploetz/mesos,kaysoky/mesos,jpeach/mesos,chhsia0/mesos,asamerh4/mesos,gsantovena/mesos,andschwa/mesos,abudnik/mesos,abudnik/mesos,abudnik/mesos,andschwa/mesos,neilconway/mesos,andschwa/mesos,verizonlabs/mesos,dforsyth/mesos,zmalik/mesos,dforsyth/mesos,gsantovena/mesos,verizonlabs/mesos,verizonlabs/mesos,zmalik/mesos,dforsyth/mesos,verizonlabs/mesos,zmalik/mesos,Gilbert88/mesos,abudnik/mesos,dforsyth/mesos,chhsia0/mesos