Ensembl gene annotations not uniform

[aiqc]

If it's possible for multiple ensembl values to be returned, then they should always be a list.

When using fields="symbol,ensembl.type_of_gene"

[
{
    'query': 'ENSG00000283341',
    '_id': 'ENSG00000283341',
    '_version': 1,
    'ensembl': {'type_of_gene': 'lncRNA'}
},
{
    'query': 'ENSG00000199352', 
    '_id': '100169751',
    '_version': 2, 
    'ensembl': [{'type_of_gene': 'rRNA'}, {'type_of_gene': 'rRNA'}], 
    'symbol': 'RNA5S1'
}
]

[aiqc]

Also, why no null value for symbol?

This forces the user to do parsing like checking for the existence of keys. just return all of the data

if 'symbol' not in list(entry.keys()):

[newgene]

@aiqc I think this issue can be resolved as described in #42, particularly this comment.