Converted coding guidelines to markdown

Clarified some examples, fixed some outdated code.

Added note about passing simple types by value.
Moved various not-so-simple methods to Bundle.cpp
Removed pointless const refs from primitive types
Minor doc wording change
Added Position::random; got rid of const refs

- Added Position::random(d) which gives a uniform random unit vector in
  d-dimensional space.
- Got rid of const refs from primitive types
- Removed Position::zero(Position): use Position::zero(pos.dimensions)
  instead.
Fixed typo