Run many tests in one go

[ivelin]

The problem

Currently storycheck takes one input md file as a command line parameter. This makes it inconvenient to run against a directory with many user stories / md files.

Desired behavior

Allow many md files to be parsed and executed in one run.
If any of them fails, the overall command should return non-zero exit code. If all tests pass, storycheck command should return 0 exit code to OS shell.

Solution

Add command line parameter --input-dir for root directory to be scanned for .md files.
Required parameter unless --input-file is provided as a parameter.

Add an optional glob command line parameter for scanning for files under the --input-dir directory. Defaults value `**/*.md'.

Produce a storycheck-summary.csv file in the --output-dir directory that will allow integration with CI workflows and monitoring tools. The CSV file would have the following columns:

input_file	outcome	results_dir
example.md	PASS	example.md.results/
example2.md	FAIL	example2.md.results/