Clean up output matchers

[mvz]

Summary

There are several matchers defined by Aruba that are very similar to matchers provided by RSpec. For example:

• include_output_string and its aliases an_output_string_including and file_content_including. These seem similar to the include or perhaps match matchers.
• include_an_object. This seems similar to include.

Expected Behavior

Aruba should use default RSpec matchers where possible to make its internal code comprehensible and to provide good examples for its users. Also, Aruba should not define generic matchers that may have to be supported beyond their internal use.

Current Behavior

There's a proliferation of matchers that increase the maintenance burden.

Possible Solution

Remove matchers that don't pull their weight.

Context & Motivation

Improving the output of failing steps is hard because there are many custom matchers that all need to be checked.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in a week if no further activity occurs.

[xtrasimplicity]

Bumped.