Unify the run-from-source guides

Now that we use bundler, these were almost identical already! Another
step to first-class citizenship for Windows.
Change remaining links to the from-source guide, add it to nav snippet
Make file paths its own page
Break out and clean up file resource page
Clean up user / group page
Change name scheme to keep files together; link in sidebar
Make nav snippet default for /windows

...and rearrange default navs into alphabetical order, while I'm at it.
Clean up the package resource page
Add PRM pages about Rack and WEBrick puppet masters

I'm not in love with the section title, but there we have it.
Add reference page about puppet agent on unix
Change name of the config_set page

This was a little confusing, since it sounded like it was about cli options
like --noop.
Edits to the rack and webrick puppet master references
Add reference page on windows agent
Minor edits to headers in unix agent page
Move resource tips and file paths sections into the PRM

Nahhh, this stuff oughtta be versioned. And there are tons of cases where we
need a *nix version of these, too. Now that the section is there, we can add to
it at our leisure.
Remove the windows/writing page; its contents are distributed elsewhere

This commit also removes the /windows nav sidebar.
Add note about negative exit codes in exec
Add notes about logging to services pages

This involved some testing and some code reading to get right. There are related
commits pending in the Puppet repo.
Be more emphatic about PE running under Rack by default
Mention reports in the agent pages