Add ability to install rbenv independently

- Can now install rbenv separately. Can be used as a requirement in a
  state for installing rbenv plugins using the git or file states
Fix description of method and whitespace lost
implement serializers
expose documentation of serializers
implement aggregation
ensure that str are yaml friendly
document aggregation
added reset tag
a little bit of lint
Made the shell shim compatible with AIX.
How to enable custom runners
Add zmqversion grain

Like saltversion, this grain can help show the effective version of a
particular component (in this case ZMQ) that is in use on the running
minion, and help aid in troubleshooting.
Check for None
salt.modules.seed: Don't die due to bad symlinks
Add CLI examples to dockerio and lxc.
Merge pull request #11016 from cachedout/doc_string_fixes

Add CLI examples to dockerio and lxc.
Fix --list all option
Merge branch 'seed' into lxc
Fix highstate output

Refs #10945
Merge remote-tracking branch 'origin/develop' into lxc