Example of parsing a CIF file

[Kolaru]

This PR adds an example of parsing a CIF file (as discussed in #13).

I used the julian way of using packages for everything, I am open to make the example dependency-free too.

[jamesrhester]

I suggest removing Manifest.toml so that users can resolve their own versions of packages.

[jamesrhester]

Thanks for this nice example, especially showing how Measurements.jl can be combined with CIF. It would be nice if the example produced some printed output when running from the shell, and instructions on running it, e.g. julia --project parse_geometry.jl or at the REPL include("parse_geometry.jl"); cif_geometry(filename).

[jamesrhester]

I've made the changes I suggested above.