v2.4.0

Added

• Added ToString(int) (by @Joy-less in #239)
• Added AsSpan(int), AsSpan(int, int), AsSpan(Range) (by @Joy-less in #239)

Changed

• Optimized and simplified Replace (by @Joy-less in #238)
• Simplified IndexOf and LastIndexOf (by @Joy-less in #238)

Fixed

• Fixed IndexOf and LastIndexOf allowing out-of-bounds index when the string to find is empty (by @Joy-less in #238)