Add id field to items table in db schema

Add lists table referenced in items table to db schema

The list is currently hard-coded to "Default" and not used anywhere,
but this schema change permits future modifications
for letting the user create multiple lists
and insert and query items in a specific list.

Explicitly use UTF-8 for text files

Update dependencies

Fix package path list in setup.py

Remove builds.sr.ht script

Add form for adding new items

Use v-if/else to toggle visibility of loading msg

Extend display to multiple items

Simplify array lookup by index fallback

Add skeleton for Vue-based web app

`vue.min.js` downloaded from the vuejs.org website.

Use PATCH instead of PUT for updating items

The item doesn't get replaced wholesale; it is only certain fields that
get updated, so PATCH is more appropriate.

Bump version -> 0.5.0

Add PUT /items/<item> handler

Improve error message for bad requests

Simplify API by using GroceryList error handling

A GroceryList.get_item() method has been added to facilitate this.

Raise Lookup- not ValueError for unknown items

Add POST /items handler

Add DELETE /items/<item> handler

Use url_for() to generate resource URLs

dictify() can no longer be easily tested, since it must be done against
a running Flask app. Thus, its test has been incorporated directly into
the `get_item` test; and the `index` test now delegates to `get_item`.