Add api summary lists to sim docs.

[ci skip]
Reorganize model docs

Moved regression and LCM docs into one page and
transition/relocation into another page. Added documentation
on model expressions, YAML files, and control totals tables.

[ci skip]
Move urbanchoice docs page under models.

[ci skip]
Small update to the utilities page

[ci skip]
Merge pull request #97 from synthicity/more-doc-updates

Model Documentation

I reorganized the model documentation so that regression/LCM share a page ("Statistical Models") and
transition/relocation share a page. I also added documentation about things like YAML files, model
expressions/formulae, and the format of control totals tables.