added non trivial examples of closures for str::find
added non trivial examples of closures for str::find

GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,graydon/rust