v0.16.9

Bugfixes, hardening and tuneups.

Fixes:

• #301
• #285

Adds GetKeyNode and GetRootNode methods to low level models. Useful for interfaces in downstream applications.
A general tuneup in various places after hammering the library as part of a larger stack of applications.

go-yaml currently panics when trying to render the test case. So we've got to short-circuit the "empty node" to not use Encode to copy across the empty scalar node, but just set the value explicitly

Removed golang.org/ x package in favour of the std lib

@ThomasRooney
@emilien-puget