calculation/edit - Edits an existing calculation.

Method parameters:
id - The ID of the calculation to edit.
expression - The new expression of the calculation.
title - The new title of the calculation.
tags - A space-separated list of tags.

Returns a JSON document of the following format:
<boolean> - Always true.

Expected errors:
CALCULATION_NOT_FOUND - A calculation with the ID doesn't exist.
ENTER_EXPRESSION - The new expression is empty.
INVALID_EXPRESSION - The new expression is invalid.
TOO_MANY_TAGS - More than 5 tags given.