Added count_vovels in string. (saw it in the python version)

[Darelife]

Description

Added a count_vovels algorithm to the string category. Uses a basic O(n) algorithms, (where n = number of characters in the string). Checks whether any of the characters in the string is 'a','e','i','o','u','A','E','I','O', or 'U'. It uses the filter() method to quickly check for it.

input.chars().filter(|c| "aeiouAEIOU".contains(*c)).count()

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

(However there seems to be a function in the cypher category that might be causing an error)