(SERVER-138) Created puppet.conf differences doc

This commit introduces a new document which contains some information
about the differences in supported settings from the `puppet.conf` file
for Puppet Server as opposed to the Ruby-based Puppet master.
(SERVER-138) Addressed PR feedback

This commit addresses some PR feedback, including:

* Reworded the language in the `ca` setting
* Added a note to the `configtimeout` setting about how Puppet agents
  still honor the setting
(SERVER-138) Set name of doc section to HttpPool-Related Server Settings

This commit changes the name of the last section in the new
`puppet_conf_setting_diffs.markdown` doc to `HttpPool-Related Server
Settings`.
(SERVER-138) Fixed typo

This commit fixes one minor typo found during a PR review.
Merge pull request #272 from camlow325/maint/master/SERVER-138-puppet-conf-setting-diffs-doc

(SERVER-138) Created puppet.conf differences doc