Add missing dependency yaml to requirements.txt

[alerque]

Imported in pantable2csv.py

[ickc]

panflute depends on YAML so depending on panflute would automatically depends on YAML.

[alerque]

Please reconsider this. Yes the panflute package also depends on YAML because it calls it, but this package's code also imports and uses yaml directly. If you were only calling a panflute function and yaml was getting loaded incidentally to that it would be okay to leave out the dependency (and let the other project pin versions if necessary). As it is this project should be calling it out as a dependency and noting which version(s) it is compatible with when necessary.

What you are suggesting is called a Transitive dependency ... except that it isn't rightly even transitive in this case because your first party code here is what imports yaml.

[ickc]

Ok, done!

[alerque]

Thanks.