Searches for a file in a dir, then the parent dir, etc.

ForEachPar invokes f in a new goroutine for each element of s and waits for all to complete.

PreviewStr returns a preview of s, which is a prefix for logging that avoids dumping a huge string to logs.

StrCat takes a bunch of strings or string slices and concats them all together into one string slice.

URLStrToMultiaddr converts a URL string like http://localhost:80 to a multiaddr.