Create matches for strout and strerr output

[acant]

Write tabular matchers to wrap the rspec output matchers
https://relishapp.com/rspec/rspec-expectations/docs/built-in-matchers/output-matcher

The output matchers are used like this:

specify { expect { subject }.to output('hi').to_stdout }
specify { expect { subject }.to output('hi').to_stderr }

And the tabular wrappers could be written like this:

input              :var1, :var2
output_stdout_with :foo,  :bar,  'foobar'
output_stderr_with :dead, :beef, 'error'

I am not sure if the better form is:

• output_stdout_with, or
• stdout_with

Or if these should be both be available and aliased.