Add support for IP connections with hostname (#14)

* Add `:ip` option to connection methods to accommodate credential
  stores that require the hostname where DNS is not available.

Handle close failures (#13)

Improve retry backoffs and ensure SSH connections are closed (#12)

Dependency updates April 2023 (#11)

Update the following dependencies to support newer Ruby versions:
* connection_pool -> 2.4
* net-scp -> 4.0
* net-ssh -> 7.1

Drop support for Ruby 2.5.

Fix connection caching and graceful closure (#10)

* Add `#close` method to all connection types
* Fix SSH gateway connection caching
* Ensure SSH gateway connections are closed gracefully before
  reinitializing a connection

Add SSH gateway support (#9)

This change adds SSH gateway support and fixes an issue where custom SSH
ports are not respected by `Remotus::SshConnection`.

Note that this change also required the test ruby version to be updated
to 3.0.4 to avoid an rspec regression where older ruby versions can no
longer handle method stubs with kwargs successfully.

Document updates for 0.4.0 release (#8)

Update the doc comments and restructure the class includes to stay
compliant with yardoc and keep our generated documentation clean.

Retry SCP failures (#6)

Add retry options for all SCP upload and download operations. This
ensures that expired connections are renewed in the same way they are
for regular SSH calls.

Resolve rexml vulnerability CVE-2021-28965 (#5)

This change resolves rexml vulnerability CVE-2021-28965 by updating gem
dependencies. Updates have also been made to require ruby 2.5+.

Ensure missing credentials are populated (#4)

This change ensures that cached credentials are only used if they have a
defined user and password. This is necessary in situations where the
cached credential may have been incorrectly populated prior to usage in
an SSH or WinRM connection.