Sensible error messages for common cases.
Sensible error messages for common cases.

Requested in #829. Handle these common errors:
 - missing name or id;
 - invalid (non-integer) id or limit;
 - no matches (results) found for the taxon name provided

OpenTreeOfLife/opentree,OpenTreeOfLife/opentree,OpenTreeOfLife/opentree,OpenTreeOfLife/opentree,OpenTreeOfLife/opentree,OpenTreeOfLife/opentree