updates Category class to query the database for the list of pages rather than the filesystem.
add idiorm to composer
update nextPage and previousPage functions to query the DB too
save to DB when saving a post to disk
add proper type filtering to Category
Adds new router which matches paths like `/notes` and `/metrics/sleep`, based on the types in the database. Post types now know how to render themselves when inside a list view (fixes https://github.com/aaronpk/p3k/issues/15)
fix lbs->kg conversion
update Site::getAllTags() to read from the database