Adding :nodoc: annotations

RDoc's TomDoc mode still includes "Internal: " methods
in the documentation, it just moves them to a different section.
Adding documentation for Format class
Updating code examples in comments
Adding trailing spaces to lines to work around RDoc

It seems to not be automatically adding a space between line
breaks in TomDoc mode, hence adding them in manually.
Adding extra documentation for Buffer class
Adding documentation for Duration class
Adding trailing spaces for RDoc
Fixing typo

Not sure where this slipped in