Implement --file-name<name> option

- can specify filename to be displayed when printing.
- useful for when piping data from STDIN

Closes #654

src/bin/bat/app.rs

@@ -222,6 +222,7 @@ impl App {
                     .transpose()?
                     .unwrap_or_else(|| vec![LineRange { lower: 0, upper: 0 }]),
             ),
+            filename: self.matches.value_of("file-name").or_else(|| None),
         })
     }
 

src/bin/bat/clap_app.rs

@@ -93,6 +93,18 @@ pub fn build_app(interactive_output: bool) -> ClapApp<'static, 'static> {
                      '--highlight-line 40:' highlights lines 40 to the end of the file"
                 ),
         )
+        .arg(
+            Arg::with_name("file-name")
+                .long("file-name")
+                .takes_value(true)
+                .number_of_values(1)
+                .multiple(true)
+                .value_name("name")
+                .help("Specify the name to display for a file.")
+                .long_help("Specify the name to display for a file. Useful when piping \
+                            data to bat from STDIN when bat does not otherwise know \
+                            the filename."),
+        )
         .arg(
             Arg::with_name("tabs")
                 .long("tabs")

src/lib.rs

@@ -129,4 +129,7 @@ pub struct Config<'a> {
 
     /// Lines to highlight
     pub highlight_lines: LineRanges,
+
+    /// Name of file to display when printing
+    pub filename: Option<&'a str>,
 }

src/printer.rs

@@ -231,7 +231,7 @@ impl<'a> Printer for InteractivePrinter<'a> {
                     InputFile::Ordinary(filename) => {
                         format!("file '{}'", filename.to_string_lossy())
                     }
-                    _ => "STDIN".into(),
+                    _ => self.config.filename.unwrap_or("STDIN").to_owned(),
                 };
 
                 writeln!(
@@ -267,7 +267,10 @@ impl<'a> Printer for InteractivePrinter<'a> {
 
         let (prefix, name) = match file {
             InputFile::Ordinary(filename) => ("File: ", filename.to_string_lossy()),
-            _ => ("", Cow::from("STDIN")),
+            _ => (
+                "File: ",
+                Cow::from(self.config.filename.unwrap_or("STDIN").to_owned()),
+            ),
         };
 
         let mode = match self.content_type {