calculation/add - Creates a new calculation.

Method parameters:
expression - The expression of the calculation.
title - The title of the calculation.
tags - A space-separated list of tags.

Returns a JSON document of the following format:
<number> - The ID of the newly created calculation.

Expected errors:
ENTER_EXPRESSION - The expression is empty.
INVALID_EXPRESSION - The expression is invalid.
TOO_MANY_TAGS - More than 5 tags given.