PDG particle data table 2019 update

[eduardo-rodrigues]

The 2019 update is out!

I need to update our CSV files with this and make 2019 the default …

This should go out in a 0.5.0 release, which should at least include the update described in #118.

[eduardo-rodrigues]

Hi @henryiii, this PR is now ready for review. All ready apart from one little thing: I put in a temporary fix in particle/particle/convert.py to generate the 2019 CSV file with updates, as otherwise Pandas would give me an error. I suspect that's because, as it is, one is effectively adding twice the file with PDG ID - LaTeX name matches. Maybe you have your preferred way to make the user LaTeX file optional when passed to the convert(...) function (my temporary fix is just a hack). Thanks.

[eduardo-rodrigues]

OK, @henryiii, I've now fixed particle.particle.convert.py making the extra LaTeX file optional.

This is ready to go in as far as I'm concerned.

[henryiii]

Looks good save for the one suggestion.