Function replaceFirst( str, regex, replacement )

Description:
Replaces the first occurrence of a regular expression in a string with a different substring value.
Parameters:
str (String)
string to manipulate
regex (String)
regular expression to match in str
replacement (String)
replacement string
Return Value (String):
same as str, but with the first match (if any) of regex replaced by replacement
Example:
replaceFirst("Messier 61", "Messier ", "M-") = "M-61"
Signature:
String replaceFirst(String, String, String)