New string functions

New functions were introduces

• trim - remove leading and trailing whitespace
• replace - replace substring by with another string
• substring - returns substring from given position
• toLowerCase - converts input to lower case
• toUpperCase - converts input to upper case
• startsWith - returns true if input strings starts with given prefix
• endsWith - returns true if input string ends with given suffix
• contains - returns true if input string contains given substring
• md5 - returns md5 hash of input
• sha1 - returns sha1 hash of input