cask manpage: Fix section header link for Environment

Remove `to_s` from some `Pathname`s.

Display formula conflict reasons

audit: Port audit_homepage method to rubocop and add tests

audit: Detect multiline and interpolated strings in formula desc cop

bin/brew: don't set blank HOMEBREW_* variables.

When creating the necessary HOMEBREW_* variables ensure that they aren't
set if their value would be empty.

docs.brew.sh: use SCSS.

audit: fix dependency option detection.

rubocop: don't always care about module length.

More environment filtering tweaks

audit: more checks for versioned aliases.

Allow --interactive to access HOME

keg: skip opt versioned aliases for devel/head.

Import style changes from:
https://github.com/Homebrew/homebrew.github.io/pull/166

Update to venv.pip_install_and_link in doc

Add autocorrect method for ComponentsOrder rubocop and tests

`venv.link_scripts(bin) { venv.pip_install buildpath }` is now `venv.pip_install_and_link buildpath`

Instead of trying to do this all with a single regex give up and do a
two stage process. Eventually I'll end up implementing a full ruby
parser here 🧌.

- only document HOMEBREW_* variables in the manpage (although still
  read from all the original environment variables).
- resort manpage environment variables in alphabetical order
- check the original path for trailing slashes

diagnostic_spec.rb: assertion in check_access_lock_dir test

Tweak troubleshooting docs and issue template

Added assertion to check `HOMEBREW_LOCK_DIR.stat.mode` changes after `HOMEBREW_LOCK_DIR.chmod 0555`

This may result in a slightly varied build but it’s generally just far
less annoying to be able to access all your e.g. shell configuration.

- Note that Homebrew Cask issues should be filed elsewhere.
- Make `brew`/homebrew-core issue differential in simpler language
- Tell people to fix all `brew doctor` issues
- Refer to the issue checklist and make it even more clear and prominent
  that we may close it out immediately if they don't use it.
- Note that proposed new issues should be widely relevant.
- Don't tell people they need to `brew cask install java`; we handle
  this in most places with a Java requirement and probably want issues
  filed where we don't.
- Remove reference to Homebrew Dupes and replace with reference to
  Homebrew Cask to try and get people filing stuff there instead.

Fixes #2608

These versioned aliases don’t correspond to the correct version if not
Installed from stable.

Fixes #2596.

Check that a required versioned alias has a valid name (rather than
assuming it’s fine based on it’s existence alone) and check for
the presence of invalid version aliases.

This should handle the case where someone bumps a formula but forgets
to rename the alias that’s mentioned in #2596.

We don't care about this in external taps as this is more about code
architecture than code style.

Travis CI tweaks.