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.

Attempt to improve Travis CI. This time without any vendoring gems
nonsense.