Support adding dataframes of metadata

[gidden]

At present, one must either add metadata from a file (load_meta()) or individually (set_meta()). We can extend one of these (probably best to do so on set_meta()) to support loading multiple metadata columns in one go.

Does anyone have an opinion before I propose an implementation?

cc @danielhuppmann

[danielhuppmann]

Sure, good idea! For completeness, you can already pass a suitable pd.DataFrame at initialization using

pyam.DataFrame(data, meta=<some meta frame>)

This is implemented here, should be just a few lines (and a test) to extend set_meta()

pyam/pyam/core.py

Line 206 in 1abb978

if meta is not None:

[gidden]

closed by #679