Features from Praekeltfoundation's fork

[Envek]

This pull request contains work by @bearnard in @praekeltfoundation's fork (permission obtained at #2 (comment)):

1. Queue sizes
2. Task retries
3. Dependencies update

After this pull request merged, I will create some more pull requests with fixes on top of it: praekeltfoundation#3, praekeltfoundation#4, praekeltfoundation#5

See discussion at #2

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To accept this PR without creating merge-commit and preserving commit SHAs (fast-forward):

git checkout master
git remote add praekeltfoundation git@github.com:praekeltfoundation/faktory_exporter.git
git fetch --all --tags --prune
git reset --hard praekeltfoundation/master
git push

This pull request will be automatically marked as merged.

It is possible because branches hasn't diverged (see network graph): @praekeltfoundation's master branch is strictly ahead of yours.

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@lukasmalkmus, thank you for your work on this exporter!

[lukasmalkmus]

Thank you for your work!