Use RegEx for parsing include lines

[studerluk]

This replaces the if/else structure for detecting and parsing include statements with a RegEx based approach.

My experiance was that it is not always clear how pandoc will split a paragraph into Elements which makes using array index for detecting include statements unreliable especially when whild cards for the paths come into play.

[DCsunset]

It makes sense to use RegEx to parse it. Thanks for your contribution.

[studerluk]

Sure, I'm glad I can help