(docs) Fix issues with the 1.7.0 readme.
(docs) Fix issues with the 1.7.0 readme.

Fixes several typos and links, and reorganizes the
`apache::mod::auth_mellon`, `mellon_enable`,
and `auth_kerb` sections, and document missing
default values.

traylenator/puppetlabs-apache,digitalmediacenter/puppetlabs-apache,puppetlabs/puppetlabs-apache,dzmitryv/puppetlabs-apache,gerhardsam/puppetlabs-apache,yakatz/puppetlabs-apache,buzzdeee/puppetlabs-apache,gerhardsam/puppetlabs-apache,samuelb/puppetlabs-apache,bmjen/puppetlabs-apache,yakatz/puppetlabs-apache,guegue/puppetlabs-apache,digitalmediacenter/puppetlabs-apache,dzmitryv/puppetlabs-apache,FlatKey/puppetlabs-apache,eputnam/puppetlabs-apache,eputnam/puppetlabs-apache,svanhart/puppetlabs-apache,guegue/puppetlabs-apache,buzzdeee/puppetlabs-apache,bmjen/puppetlabs-apache,puppetlabs/puppetlabs-apache,traylenator/puppetlabs-apache,samuelb/puppetlabs-apache,FlatKey/puppetlabs-apache,svanhart/puppetlabs-apache