Add source_files and task_name options

[miff2000]

This PR adds these two new settings which can be passed into the Action

• source_files allows a list of specific files to scan to be provided
• task_name allows a specific task to be executed

[miff2000]

Actually, if it's preferred, I could add an extra_flags option which would allow any arbitrary options to be passed to PySpelling instead?

[jonasbn]

Hi @miff2000

I will have a look at the PR and will get back to you. I plan to review it tomorrow.

[miff2000]

This looks good, I might apply some additional changes, primarily on the documentation parts - I hope this is okay.

Thank you for you contribution

I've just added a merge commit to add your updates in :) Thanks for the quick turnaround!

[jonasbn]

This is included in release 0.10.0, thank you for your contribution

[edumco]

This PR closes #33