In disk_build:

In disk_build:
* Write deps file in indented rather than minified JSON

In jst_server:
* Change to ES6 modules
* Change to fsPromises
* Change to ES6 classes
* Remove unneeded dependencies
* Use Problem object internally instead of Server.die() and Site.die()
* For API endpoints, serve the JSON-encoded Problem object directly

In ndcode_site:
* Rework /my_account/sign_up/index.html.jst to use custom validation style, reduce to 2 steps (former steps 1 and 2 are now done together and resulting message is displayed in red underneath the step 1 buttons), and improve placeholder text
* Implement draft updating thread in /my_account/sign_up/index.html.jst (avoids possibility of concurrent draft updates), use oninput rather than onchange event
* Add random placeholder data generator (persists in session for 24 hours)
* Disable the "Create account" button and null draft when sign up form is blank
* In /my_account/sign_up/index.html.jst use HTML5 hidden attribute, not jquery
* In /my_account/sign_up/index.html.jst improve tick, cross, spinner, message
* Make tick, cross and spinner have no height, so they don't affect card header
* More comprehensive system for displaying icons vertically centred within text
* In /my_account/sign_up/index.html.jst add icons to every button
* Fix unnecessary extra syntax in /_config/Problem.mjs
* In /my_account/sign_up/index.html.jst use variables id_XXX instead of document.getElementById(), and add a script /ids.sh to easily create definitions for them
* In /my_account/sign_up/index.html.jst change placeholder for captcha text to xxxxxx (because the randomized value was too confusing), fix some minor bugs
* In /my_account/sign_up/index.html.jst improve layout around verification code
* Consistency changes for the Problem object
* Use jst_server.Problem everywhere, make /_lib/post_request.jst use jst_server's new error handling to serve the JSON-encoded Problem instead of doing it itself
* Change all the get_draft.json endpoints to be like sign_up one (simpler because the JSON from the database is returned directly, including the expires field)
* Update /my_account/verify_email/index.html.jst to latest way, no accordion
* Update /my_account/password_reset/index.html.jst to latest way, no accordion
* Update /my_account/verify_password/index.html.jst to latest way, no accordion
* Update /my_account/send_verification_email/index.html.jst to latest way, no accordion and now an inline form (need to improve label spacing when collapsed)
* Update /contact/index.html.jst to latest way, no accordion, placeholder company
* In /_lib/navbar.jst prefix all ids with navbar- for uniqueness
* In /_lib/navbar.jst use variables id_XXX instead of document.getElementById()
* In /lib/navbar.jst use HTML5 hidden attribute and remove some other jQuery
* In /lib/navbar.jst rework feedback to be similar to /contact/index.html.jst way
* In /lib/navbar.jst rework sign in to be similar to feedback
* Remove modal fade because of an annoying glitch during fade in/out (it seems to move slightly in the horizontal, which may be because of scrollbar visibility)

In sass_css_cache:
* Send style option to SASS to produce minified CSS output