add date-based versioning

brew: set Bintray variables.

These are set as `HOMEBREW_BINTRAY_*` and then used by the rest of
`brew` as normal.

Fix audit version_scheme and revision checks.

Another attempt at fixing `brew audit` issues around detecting
`revision` and `version_scheme` changes correctly. First done in #1754
and #2086 (reverted in #2099 and #2100).

To ease future debugging a `ph` helper has been added to print a hash
and a series of RSpec tests to verify that the `revision`,
`version_scheme` and `version` formula version audits behave as
expected.

Fixes #1731.

Fix and remove various TODOs.

Fix those that can be done so without tearing Homebrew to pieces and
remove the comments for those that can never be done.

Hide sensitive tokens from install/test/post.

Install uninstall messages

It's used by ENV.fortran.

Fixes https://github.com/Homebrew/brew/issues/2530
Fixes https://github.com/Homebrew/homebrew-science/issues/5485

Fixes https://github.com/caskroom/homebrew-cask/issues/32840.
Fixes https://github.com/Homebrew/brew/issues/2529.

Refactor cask metadata directory methods.

tap: warn on tapping deprecated, official taps.

utils: fix which_editor.

readall: check for shadowed aliases.

More deprecations.

Handle when there's no editor variable specified or it's specified but
empty.

travis.yml: cache Bundler output.

If an alias has the same name as a formula then weirdness will result
so ensure this causes `readall` to fail.

audit: flip GNU mirror preference.

They don't contain any formulae so tapping them will add pointless
clutter.

Hide these tokens to avoid malicious subprocesses e.g. sending them
over the network. Also, support using these tokens with environment
filtering and clear `HOMEBREW_PATH` from subprocesses to stop them
sniffing it. Finally, use `HOMEBREW_PATH` to detect Homebrew’s user’s
PATH for e.g. `brew doctor` etc.

Deprecate more methods. Internal APIs have been verified to be unused
elsewhere and removed. External APIs have had deprecation methods added.
Existing deprecations have been either upgraded to produce warnings or
no longer deprecated and the reasoning documented.

Travis needs some coaxing to find where we put it. This should improve
build reliability due to network issues.

audit: lookup unversioned formulae with Formulary.

tests: reduce some noise.

Now that both the primary and mirror URLs use HTTPS we can flip these
around so the primary URL is the primary URL and we don't have problems
with waiting for mirror propagation.

This means that if e.g. the unversioned formulae exists in another tap
this audit won't produce a false positive.

- Tweak the way offline skipping happens
- Skip more tests that break when offline
- Hide more stdout output from tests.

formula_installer: remove feature flags.

Fix `brew edit` with environment filtering.

Validate `container :type`.

[trifle] missing space

audit: ensure default dependencies don't use options.

audit: new formulae should not require patches.

We've been testing the recursive dependency check and allowing unlinked
dependencies in CI for a while with no adverse consequences so enable
them globally now for all users.