Normalize export style in problem.md

also problem.md markdown cleanup
closes #45

### What I did
* Fixed up export style as discussed
* Made h2 style consistent (took out superfluous wrapper hash marks: markdown parser sets these apart in blue already)
* Removed superfluous newlines at start/end of code blocks
* I moved "boilerplate" section to the end of each problem.md for consistency

### Ongoing issues
* Some of these are way too long (part of reason I shortened h2 syntax)
* Style is inconsistent: some start with # Task, some have lots of intro etc.. this should be standard (is there a styleguide for this?)
* order of sections should be consistent