Added --stdin-data argument

This argument accepts a path to a file. The data contained in the file will be passed to the command via stdin.

Closes sharkdp/hyperfine#541

src/error.rs

@@ -53,4 +53,6 @@ pub enum OptionsError<'a> {
     ShellParseError(shell_words::ParseError),
     #[error("Unknown output policy '{0}'. Use './{0}' to output to a file named '{0}'.")]
     UnknownOutputPolicy(String),
+    #[error("File containing stdin data '{0}' does not exist")]
+    StdinDataFileDoesNotExist(String),
 }