Use tagged releases to check versions easier

[mtlynch]

It would be helpful if vdesktop supported tagged releases so that users could see when there were major upgrades and what the changes are between versions. It would also make it easy for users to stick to a particular version instead of relying on a branch name like old-version.

This would allow you to get rid of the version file and do version checks like this:

Check local release version

git tag | tail -n 1

Check latest tagged release from Github

curl \
  --silent \
  --show-error \
  --header "Accept: application/vnd.github.v3+json" https://api.github.com/repos/Botspot/vdesktop/releases \
  | python3 -c "import sys, json; print(json.load(sys.stdin)[0]['tag_name'])"

[mtlynch]

Whoops, Github gave me an error when I first tried to post. Deleting this dupe (see #14).