Implement our fancy new --help output (#3883)

* Start reorganising -h output

* Fix the --debug flag

  - Currently exceptions are often caught and burried in log files, even
    if this flag is provided!

* Explain the insanity

* Parallalelise nosetests from tox (#3836)

* Parallalelise nosetests from tox

* Parallelise even more things, break even more things

* Now unbreak all the tests that aren't ready for ||ism

* Try to pass tests!

 - Remove non-working hack in reporter_test
 - also be selective about ||ism in the cover environment

* Try again

* certbot-apache tests also work, given enough time

* Nginx may need more time in Travis's cloud

* Unbreak reporter_test under ||ism

* More timeout

* Working again?

* This goes way faster

* Another big win

* Split a couple more large test suites

* A last improvement

* More ||ism!

* ||ise lint too

* Allow nosetests to figure out how many cores to use

* simplify merge

* Mark the new CLI tests as ||izable

* Simplify reporter_test changes

* Rationalise ||ism flags

* Re-up coverage

* Clean up reporter tests

* Stop modifying testdata during tests

* remove unused os

* Improve the "certbot certificates" output (#3846)

* Begin making "certbot certificates" future safe

* Handle the case where a renewal conf file has no "server" entry

* Improvements, tweaks

* Capitalise on things

* Print the command summary for -h and -h all, but not otherwise

Also, update nginx not installed CLI hint

* Add a "certificates" help section

* Clean up usage string construction

* Greatly improve "certbot -h TOPIC"

  - subcommands now get their own usage headings if they want them
  - added "certbot -h commands"

* A few more cli formatting tests

* Auto-populate the verb subgroups from the docs

* Show the new help output

* Lint, tweak

* More lint, and cleanup

* Infinite lint

* Add rename to command summary; sort "-h commands" output

* Use fancy string formatting

* More space

* Implement --help manage

Also, implement a general mechanism for documenting subcommands within
topics

* Remove one comma

* Only create weird parser structures if -h is provided :)

* Update sample cli out

* Lint

* Revert cli-help.txt to previous release version

* Grammar & style