improvement on the use-cases of the batch query endpoint with field-level weights

[newgene]

e.g.

mg.querymany(['Tmem27', 'TYMP'], scopes='symbol,alias', species='human', size=1) mg.querymany(['Tmem27', 'TYMP'], scopes='symbol^10,alias', species='human', size=1)

We should better document this use- case (with custom field-level weights), adding query examples, etc.

also size parameter should be aliased and documented as max_hits.