* Convert documentation files to Markdown
* Add notice about models not being annotated by default to changelog in 3.0

Looks like it's breaking in Github CI because Ruby 2.3.X is no longer supported by `actions/setup-ruby@v1`. Ruby 2.3.X has stopped being supported since March of 2019, so I've removed Ruby 2.3.X versions from both Github and Travis CI.

It's also breaking in Travis CI because it's timing out in an interactive prompt when trying to do `gem update --system`. This is due to changes to [Ruby Gems 3.1.1](https://github.com/rubygems/rubygems/issues/3036). This has been fixed.

Failing Github CI build: https://github.com/ctran/annotate_models/runs/335456181
Failing Travis build: https://api.travis-ci.org/v3/job/625759725/log.txt

ActiveAdmin defaults to false.  Add `active_admin` option so people using this gem can more easily enable annotating files in `app/admin`.

Rails 6 has dropped name from ActiveRecord::ConnectionAdapters::ForeignKeyDefinition
for Sqlite3 adapter:

https://github.com/rails/rails/blob/f2df77709f7e536aaf4d6f984ff21a49d44d34c1/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb\#L305-L311

This has caused issues with getting foreign key info and blowing up
when trying to annotate models with foreign keys. This commit
adds one additional check for name presence and uses column
attribute from options instead.

Closes #620.

Updates the readme to include a note about upgrading the gem to version 3 and that it can default to doing nothing.

Reverted tag to to use `v*` prefix instead of `release/v*`.

Bumps [loofah](https://github.com/flavorjones/loofah) from 2.3.0 to 2.3.1.
- [Release notes](https://github.com/flavorjones/loofah/releases)
- [Changelog](https://github.com/flavorjones/loofah/blob/master/CHANGELOG.md)
- [Commits](https://github.com/flavorjones/loofah/compare/v2.3.0...v2.3.1)
Signed-off-by: dependabot[bot] <support@github.com>

Setting the default to annotate models as it is the main feature of the gem

Based on the official docs:

https://help.github.com/en/articles/configuring-a-workflow#adding-a-workflow-status-badge-to-your-repository

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.6.6.2 to 1.10.4.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sparklemotion/nokogiri/compare/v1.6.6.2...v1.10.4)
Signed-off-by: dependabot[bot] <support@github.com>

Updates the requirements on [rake](https://github.com/ruby/rake) to permit the latest version.
- [Release notes](https://github.com/ruby/rake/releases)
- [Changelog](https://github.com/ruby/rake/blob/master/History.rdoc)
- [Commits](https://github.com/ruby/rake/compare/v10.4.0...v13.0.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Before, whenever a new file is added to `lib`, the contributor or
maintainer has to remember to explicitly add it to the gemspec. If this
step is forgotten, it results in a broken release, like #657.

This commit makes this process less error prone by using `git ls-files`
to automatically include all appropriate files in the gem. This is in
line with what is advocated by Bundler's gem template:

https://github.com/bundler/bundler/blob/2a4d88a7044528209321fd4441e995ec66f604b9/lib/bundler/templates/newgem/newgem.gemspec.tt#L26

Add opening parenthesis

Currently the gem released as version 3.0.0 is broken. Fixes #657 

The gem is missing constants.rb and parser.rb file

Changed references to `--additional_file_patterns` to be `--additional-file-patterns` to make it consistent with other flags.

Adds tests for `.include_routes?`, `.include_models?`, `.skip_on_migration?`. Also moves the `TRUE_RE` under the `Annotate::Constants` namespace.

Updating tested ruby versions to use latest versions.

* Bump ruby 2.4.6 -> 2.4.7
* Bump ruby 2.5.5 -> 2.5.6
* Add ruby 2.6.4
* Remove old versions of 2.6.X

Prior to this change, `Annotate.include_models?` returned the inverse of `Annotate.include_routes?`. This made it so annotating models and routes was not possible to do together.

This PR adds an explicit `--models` flag and also adds it the option to `lib/generators/annotate/templates/auto_annotate_models.rake` with the default being set to `false`. 

Fixes #563 and undoes the bug introduced in #485.

In looking into #563, I realized there are gaps in test coverage. For example, `bin/annotate` doesn't have any tests. 

Tidying the spec directory to make it easier to add tests in future work.

Add better documentation for new option for additional file patterns. Implemented in #633 and #636.