Rewrite and simpify algorithms to avoid iteration

This commit rewrites the Algorithms section with the intention of making
it simpler to understand and closer to how implementations will likely
be written. Previously, whether a settings object is a secure context or
not was determined by walking the entire creator chain examining HTTPS
state etc. on each creator. The new algorithms now simply looks at the
immediate creator (if any) and checks that it is a secure context before
checking HTTPS state etc. on the settings object that is the subject of
the algorithm. In other words the algorithm now relies on recursion
instead of iteration. This does away with the need for the 'Gather
document’s relevant ancestors' section and simplifies the 'Is settings
object a secure context?' section.