Get extra metadata from meta.yam instead of extra.yaml
Get extra metadata from meta.yam instead of extra.yaml

Closes #39

astropy/conda-builder-affiliated,mwcraig/conda-builder-affiliated,astropy/conda-build-tools,mwcraig/conda-builder-affiliated,astropy/conda-builder-affiliated,Cadair/conda-builder-affiliated,Cadair/conda-builder-affiliated,astropy/conda-build-tools