Move to Remark for markdown parsing

[sambauers]

See original conversation on #74

This PR covers all tests, currently working on updates to website documentation to align with new markdown plugin pattern.

[sambauers]

Note that I have left one test failing due to Remark issue remarkjs/remark#497

[sambauers]

Some sort of build issue at Travis. I was expecting it to fail, but only because there is one broken test. Seems it can't complete yarn build:js due to a missing babel module. Not sure what to do about that.

[dominikwilkowski]

I'll have a look and go through the code and commit some stuff into this.... should be good to merge soon
Thanks for the work :D

[dominikwilkowski]

Make sure you don't make this PR too big. Like I said in the issue best to not do any tests for now or any other things like config options and we go from there

[sambauers]

Make sure you don't make this PR too big. Like I said in the issue best to not do any tests for now or any other things like config options and we go from there

Oh, too late. I got carried away. I also had to bypass my prior markdown-it implementation, so I ended up copying changes to a new repo without history. So it ended up one big commit basically.

If it helps, most of the changes are in src/parse.js, specifically in ParseMD(). I did have to modify config loading to allow for a nested object in the markdown options.

Impacts on tests was mostly differences in treatment of whitespace, and Remark has more relaxed entity encoding. There were some other places where existing renderer implementation may not have been catching everything it should have been, or maybe was too aggressive. So there are small modifications there.