Feature: cast to number from string

[vlushn]

It is currently not possible to generate a numeric string and then convert it to a number.

Sample use-case: generating a date-time and using that to calculate the week number and converting to number

Implementation-wise, this functionality probably does not directly belong to number either because you would need to add cases for all the subtypes of number. Perhaps adding a more generic cast/conversion facility would be benificial (string -> bool, or number -> datetime etc.)