Migrate pg:ps, pg:kill, and pg:killall from pg-extras

Graduate some pg-extras commands into the main CLI

- ps: view active queries with execution time
- kill: kill a query by pid
- killall: terminates *all* connections to the database
clean up some of the pg-extras move. closes #853
2.40.0
Fix typo in docstring
resume the crusade against underscores.
Unregister commands made private after the fact.

Commands are registered on method_added, but when a method is made private after defined, there's no way to tell that happened.

(Trust me. Ruby has no hook for visibility change and overriding Module.private breaks it for calls with no args.)

So once all commands are loaded we scan for commands whose methods that have turned private and remove them.

Sudo uses aliasing extensively and was leaking a bunch of methods as invalid commands.
always alias commands with underscores to dashes

the command in the help comment should always be given as the dash version for help purposes
Exclude add-on plan from post provision docs msg
Remove unnecessary guard from add-on name extraction
v2.40.1
fix update urls, point to heroku.com instead of herokuapp
fix excon extension, also follow 301 redirects!
Show cache_size in apps:info if present.
remove debugging
support -c, like psql
Add destructive action warnings to SSL Endpoint commands
Update copy for certs:update
Fix specs + add new ones for confirmation
Merge pull request #900 from heroku/brandur-ssl-endpoint-destructive-actions

Add destructive action warnings to SSL Endpoint commands
Allow `--endpoint` option

This pull re-enables the `--endpoint` option available on select `certs`
commands which allows a customer with multiple endpoints to operate on
one in particular (this is now a legacy state). This help text is
required for the option parser to respect the particular option.