Fixed donate button
Fixed GH#77: line break inside inline math statement confused parser
Now using minitest for tests
Allow a template to be applied before, after or before and after
Allow the template option itself to contain the template instead of referencing a file
Fixed problem with line breaks in GFM parser

Line break insertion directly in the paragraph parser didn't work
correctly because it split up lines into separate :text elements
which lead to problems parsing multiline span elements.
Unknown option keys are now simply passed through and not removed anymore
Added basic PDF converter based on the prawn PDF generation library