add progressmeter

[floswald]

add https://github.com/timholy/ProgressMeter.jl

[JulienPascal]

I am really much willing to do this PR. ProgressMeter adds a really fancy touch to this package.
But should I wait until Edoardo's PR is merged?

[floswald]

Yes t depends on #25! Currently working on that. I have an issue with the jld2 part in fact.