Consolidate schema loading sections

[handrews]

We are adding a section dealing with loading, processing,
and referencing schemas.

These sections have been moved without any changes to text or
formatting beyond adjusting the indentation to fit the new
location.

This is the first step for #849.

[handrews]

@gregsdennis @johandorland @Julian tagging y'all in as implementors to see if this direction makes sense. See #849 for context- this PR is just moving blocks around unchanged so if possible I'd like to get it merged quickly so I can put up actual real changes for longer review.

[Julian]

The outline in #849 certainly seems to make sense to me if I understand it (which there's always a chance I don't when dereferencing is involved). So +1 on this one I think?

[gregsdennis]

These seem like the appropriate sections. Lift-and-shift doesn't concern me so much as the changes that'll come later to make it read a bit more fluently (to suggest that these parts are supposed to be together).

[Relequestual]

git diff master handrews/load --color-moved --color-moved-ws=allow-indentation-change
All changes are moves. Good to go.

[Relequestual]

We shouldn't worry about xml2rfc complaining about figure length as the resuling text document does the right thing when wrapping.

[handrews]

@Relequestual yeah the length warnings are not new.

@Julian I ended up including the part on dereferencing in the new section because the question of how to resolve references is closely related to the question of what it means to "load" a schema so that you have it available to reference.