Message History and Timestamps

Merge pull request #20 from tblanarik/message_log

Keeps a running log of messages, now with timestamps

Reduced Chatter

SpotBot now uses the Azure Storage Account that's already attached to the Azure Function it runs in to store the last message posted for each callsign. This is used to decide to either update the previous message (if it's recent) or post a new one - reducing the amount of chatter when a radio operator is changing bands/modes or respotting.

Deeplink to SOTA/POTA site

The bot now posts a link to the callsign's POTA or SOTA page, eg:

KI7HSG | pota | freq: 21.355 | mode: ssb | loc: US-4555 | [See their latest spot](https://api.pota.app/spot/comments/KI7HSG/US-4555)

First version

First version