Add notebook illustrating conversion of CHEMKIN files via ck2yaml

[ischoegl]

This PR collects CHEMKIN input files previously used in Cantera (i.e. < version 2.5.0a4) and re-creates the following YAML files from scratch.

GRI-Mech 3.0 derived:

• gri30_demo.yaml (corresponds to gri30.yaml without deprecated phases)
• h2o2_demo.yaml (corresponds to h2o2.yaml)
• air_demo.yaml (corresponds to air.yaml)
• argon_demo.yaml (corresponds to the - now deprecated - argon.yaml)

NASA derived:

• airNASA9_demo.yaml (corresponds to airNASA9.yaml)
• nasa_demo.yaml (corresponds to nasa.yaml)

Motivation:

The example serves two purposes:

1. Illustrate usage of ck2yaml
2. Document heritage of input files

Other:

• Comments are currently rudimentary; if this PR is of interest, they will be augmented.
• Some of the original input files were missing a header block, which was added for clarity. If Add --extra option to ck2yaml cantera#794 (--extra option) is merged, this change can be reversed, while still creating a header that corresponds to stock cantera yaml input.

[bryanwweber]

@ischoegl Does this need to be updated to resolve your comments above about Cantera/cantera#794?

[ischoegl]

@bryanwweber ... it likely does. With all that time passing I had honestly forgotten about this. Shouldn’t take too long, but it’s not a priority for me at the moment.

What’s the current game plan for 2.5? (I noticed that PR review activity slowed down on the main repo). I was hoping for the HDF5 review as the pandas solution is sub-optimal ... other than that, I’m mostly done with my contributions.

[bryanwweber]

Yeah, no problem if this takes a little while. I'm working on a burn down list of high-priority stuff for 2.5, my objective is to get a beta out ASAP... Subject of course to other work interfering, as always 😁

[ischoegl]

@bryanwweber ... Good to know. Any chance to get Cantera/cantera#840 reviewed and added prior to beta? It’d be good if the stand-in HDF implementation never makes it to beta. I think that @speth’s comments in Cantera/cantera#830 do have a point.

[ischoegl]

@bryanwweber ... I updated this PR (i.e. instead of updating header blocks, I used the --extra option)