No need to use Option for boolean values.

This commit simplify the code without changing the logic.
I use [this trick](TeXitoi/structopt#93 (comment)) to be able to define a default value for a boolean field.

src/main.rs

@@ -1,15 +1,14 @@
-use structopt::StructOpt;
+use app::UI;
+use core::time;
 use std::time::{SystemTime, UNIX_EPOCH};
+use structopt::StructOpt;
 use termion::async_stdin;
 use termion::input::TermRead;
-use app::UI;
-use core::time;
-
 
 mod app;
 mod plotting_utils;
-mod widget_progress_bar;
 mod widget_main_chart;
+mod widget_progress_bar;
 mod widget_text_output;
 
 static ONE_BILLION: f32 = 1000000000.0;
@@ -22,11 +21,15 @@ struct Cli {
     #[structopt(short = "t", long = "target")]
     target_result: Option<f64>,
 
-    #[structopt(long = "show-regression-line")]
-    show_regression_line: Option<bool>,
+    #[structopt(
+        long = "show-regression-line",
+        parse(try_from_str),
+        default_value = "true"
+    )]
+    show_regression_line: bool,
 
     #[structopt(long = "show-target-line")]
-    show_target_line: Option<bool>,
+    show_target_line: bool,
 
     #[structopt(short = "l", long = "history-len", default_value = "100")]
     history_len: usize,
@@ -42,20 +45,23 @@ fn main() {
         &args.command,
         args.target_result,
         args.history_len,
-        args.show_regression_line.or(Some(true)).unwrap(),
-        args.show_target_line.or(Some(false)).unwrap()
+        args.show_regression_line,
+        args.show_target_line,
     );
     let mut keys = async_stdin().keys();
 
-    loop{
-        let current_time = SystemTime::now().duration_since(UNIX_EPOCH).unwrap().as_secs_f64();
+    loop {
+        let current_time = SystemTime::now()
+            .duration_since(UNIX_EPOCH)
+            .unwrap()
+            .as_secs_f64();
         if refresh_rate.as_secs_f64() < current_time - last_time {
             ui.evaluate();
             last_time = current_time;
         }
         if !ui.event_handler(keys.next()) {
             ui.clean_up_terminal();
-            break
+            break;
         }
-    }  
-}
+    }
+}