Add CLI integration tests

[JamyGolden]

Tests included

test_operation_render_no_data

Tests render with no data

test_operation_render_single_data

Tests render with a single --data flag

test_operation_render_multiple_data

Tests render with multiple --data flags

test_operation_render_single_datafile

Tests render with a single --data-file flag

test_operation_render_multiple_datafile

Tests render with a multiple --data-file flags

test_operation_render_mixture_of_data_and_datafile

Tests render with a mixture of --data and --data-file

test_operation_render_using_stdin_as_template

Tests render using stdin and providing - as the template path

test_operation_render_out

Tests render with the --out flag