GetFileHash returns the hex encoding of the sha-256 hash of the file at the specified path.

NoCache disables browser caching.

ParseFileSize converts a string contains a positive integer and an optional KB/MB/GB unit to int64, or returns error.

Trim string to numChars: we only care about the number of runes (encoded characters of variable bytes) so we don't cut up multibyte characters.

ZipFiles creates a zip archive per the options and writes to the writer.

ZipOptions is a set of options for ZipFiles.