regroup puppet how-to into broader sections

That "howto" section was getting really unwieldy.

Before:

 - Modifying an existing configuration
 - Adding a new module
 - Contributing changes back upstream
 - Running tests
 - Validating Puppet code
 - Listing all hosts under puppet
     - Other ways of extracting a host list
 - Running Puppet everywhere
 - Batch jobs on all hosts
 - Progressive deployment
 - Adding/removing a global admin
 - Examining a Puppet catalog
     - List resources by type
     - View/filter full catalog
 - Troubleshooting
 - Consult the logs of past local Puppet agent runs
     - Running Puppet by hand and logging
     - Finding exported resources with SQL queries
     - Finding exported resources with PuppetDB
 - Password management
 - Getting information from other nodes
     - Exported resources
     - PuppetDB lookups
     - Puppet query language
     - LDAP lookups
     - Hiera lookups
 - Revoking and generating a new certificate for a host
 - Pager playbook
     - [catalog run: PuppetDB warning: did not update since \...\]
     - Problems pushing to the Puppet server
 - Disaster recovery

31 entries, 17 top level, 14 second.

After:

 - Programming workflow
     - Modifying an existing configuration
     - Adding a new module
     - Contributing changes back upstream
     - Running tests
     - Validating Puppet code
 - Puppet tricks
     - Password management
     - Getting information from other nodes
         - Exported resources
         - PuppetDB lookups
         - Puppet query language
         - LDAP lookups
         - Hiera lookups
     - Revoking and generating a new certificate for a host
 - Deployments
     - Listing all hosts under puppet
     - Other ways of extracting a host list
     - Running Puppet everywhere
     - Batch jobs on all hosts
     - Progressive deployment
     - Adding/removing a global admin
 - Troubleshooting
     - Consult the logs of past local Puppet agent runs
     - Running Puppet by hand and logging
     - Finding exported resources with SQL queries
     - Finding exported resources with PuppetDB
     - Examining a Puppet catalog
         - List resources by type
         - View/filter full catalog
 - Pager playbook
     - [catalog run: PuppetDB warning: did not update since \...\]
     - Problems pushing to the Puppet server
 - Disaster recovery

34 entries, 6 top level, 23 second level, 7 third level

The caveat here is that the "third level" here is actually a *fourth*
level, something which we're typically trying to avoid, but in this
case this is not really a possibility.