Do the usual deprecate/disable dance for the Homebrew 2.6.0 release.

Not to be merged until the next release will definitely be 2.6.0.

This API authentication path will be disabled on Nov 13 2020.

- A user reported the following error when running `brew gist-logs`,
reproducible with any formula:

```
$ brew gist-logs rustup-init
Error: undefined method `length' for nil:NilClass
Please report this bug:
  https://docs.brew.sh/Troubleshooting
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/cmd/gist-logs.rb:145:in `gist_logs'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/brew.rb:102:in
```

- From what I can tell, `gist_logs_args.parse` had ended up in the wrong
  method. The `gistify_logs` method already has `formula` (ie the
  formula name) passed into it. But it's the `gist_logs` method that needs
  to do the argument parsing. This was discovered by looking at some other
  recently changed ARGV => Homebrew.args code like cmd/info.

Use active voice when applicable, better verbs & adjectives, preposition usage, proper tense, etc.

Reorder switches as force/quiet/verbose/debug, --installed before --all, and link to SPECIFYING FORMULAE from top of page.

Freeze the results changed in #6072.

Fixes #5586

- Make `gist-logs` perform more checks
- Don't complain about a non-/usr/local install at install time unless
  actually building from source.
- Show more checks output on a build error
- Improve naming of checks methods

While working on f10691bc, I noticed this odd comment and decided to
investigate. I wasn't able to reproduce the undesirable behavior because
I cannot get 1.8.7 to compile with rvm but I did notice through some
testing that iTerm2 displays a lock character when echo mode is
disabled. My intent had been to remove this method because Homebrew has
moved past a Ruby version that would necessitate the "hack" but this
method's behavior is actually desirable today, so I changed the comment
to remove the potential flag and instead left a comment explaining
a good second reason for the method.

Co-Authored-By: JBallin <JBallin@users.noreply.github.com>