Changes

Fixed a locale bug with the windSpeed and windGust float values by using toString() instead of format(). This is backwards compatible with weewx 3.8.2
Fixed a bug where MQTT AJAX page updates weren't in locale decimal. (e.g. comma instead of period for decimal). Can't use parseFloat() on it's own if the culture is a comma for decimals. Need to use toLocaleString(). This requires converting the string to an int, to a float, back to a string.
Fixed a bug with the chart gapSize on the day charts to use the archive_interval and not an arbirary 5 minute setting.
Fixed a bug with windDir vectors not being consistent.
Fixed a bug with the forecast breaking the page if it wasn't enabled, but MQTT Websockets was.
Fixed a bug with DarkSky visibility units, since they don't seem to provide this themselves. So it's their bug that I'm trying to work around.
Now the charts use the system locale decimal point.
Update non-MQTT page timestamp to use moment.js to fall in line with other datetime stamp locale formatting.
On the front page, if both charts are hidden, hide the full row to save on whitespace.
On the charts page hide the chart if it's hidden in skin options.

Install

If you are upgrading, while unlikely something will go wrong, please make sure you have a backup your configuration.

wget https://github.com/poblabs/weewx-belchertown/archive/weewx-belchertown-0.9.1.tar.gz

Then run

sudo wee_extension --install weewx-belchertown-0.9.1.tar.gz

Configure the weewx.conf pre-requisites and restart weewx when done.

Please report any issues you find here. This helps me keep track of them.