added ToLower string extension method (can lower specific indexes of string)
added ToLower string extension method (can lower specific indexes of string)

original commit: vintage-software/vstack@ebf39b8622ed5794676552f77b2b9a7b43c0d6e2

split from c6fca7538104765e971ddcffb726409d29f245e2

vintage-software/vstack