Make Saaze build two times faster by using MD4C

[eklausme]

Saaze has some design criteria, see Saaze Introduction:

1. Easy to run
2. Easy to host
3. Easy to edit
4. Easy to theme
5. Fast and secure
6. Simple to understand

When adding a PHP FFI interfaces, clearly, requirement 1+2 would suffer, but 5 would increase twofold.

I changed the Markdown to HTML conversion from Markdown Extra to MD4 and observed a 50% CPU time reductions overall.

I wrote about this here: Calling MD4C from PHP via FFI.