Expand tabs to spaces; add ProgressStyle::with_tab_width

Tab width in terminals is not standardized (though 4 or 8 spaces seems common)
but this provides an escape hatch.

This should fix #150.

src/style.rs

@@ -23,6 +23,7 @@ pub struct ProgressStyle {
     // how unicode-big each char in progress_chars is
     char_width: usize,
     format_map: HashMap<&'static str, fn(&ProgressState) -> String>,
+    tab_width: usize,
 }
 
 #[cfg(feature = "unicode-segmentation")]
@@ -91,6 +92,7 @@ impl ProgressStyle {
             char_width,
             template,
             format_map: HashMap::default(),
+            tab_width: 4,
         }
     }
 
@@ -140,6 +142,12 @@ impl ProgressStyle {
         self
     }
 
+    /// Sets the number of spaces to which tabs will be expanded. Default: 4
+    pub fn with_tab_width(mut self, tab_width: usize) -> ProgressStyle {
+        self.tab_width = tab_width;
+        self
+    }
+
     /// Sets the template string for the progress bar
     ///
     /// Review the [list of template keys](./index.html#templates) for more information.
@@ -327,6 +335,8 @@ impl ProgressStyle {
                         continue;
                     }
 
+                    buf = buf.replace('\t', &" ".repeat(self.tab_width));
+
                     match width {
                         Some(width) => {
                             let padded = PaddedStringDisplay {
@@ -348,7 +358,9 @@ impl ProgressStyle {
                         },
                     }
                 }
-                TemplatePart::Literal(s) => cur.push_str(s),
+                TemplatePart::Literal(s) => {
+                    cur.push_str(&s.replace('\t', &" ".repeat(self.tab_width)))
+                }
                 TemplatePart::NewLine => lines.push(match wide {
                     Some(inner) => {
                         inner.expand(mem::take(&mut cur), self, state, &mut buf, target_width)
@@ -398,7 +410,7 @@ impl<'a> WideElement<'a> {
                 buf.write_fmt(format_args!(
                     "{}",
                     PaddedStringDisplay {
-                        str: &style.message,
+                        str: &style.message.replace('\t', &" ".repeat(style.tab_width)),
                         width: left,
                         align: *align,
                         truncate: true,