Add argument ranges and defaults to command line help text. (#74)

* Add argument ranges and defaults to command line help text.

* Update cmdapp/src/main.rs

Co-authored-by: Viktor Szakats <vszakats@users.noreply.github.com>

---------

Co-authored-by: Chris Tsang <chris.2y3@outlook.com>
Co-authored-by: Viktor Szakats <vszakats@users.noreply.github.com>

Author: 3 people

cmdapp/src/main.rs

@@ -68,45 +68,45 @@ pub fn config_from_args() -> (PathBuf, PathBuf, Config) {
             .long("filter_speckle")
             .short("f")
             .takes_value(true)
-            .help("Discard patches smaller than X px in size"),
+            .help("Discard patches smaller than X px in size. Accepts integer values within the range [0, 16](Default: 4)"),
     );
 
     let app = app.arg(
         Arg::with_name("color_precision")
             .long("color_precision")
             .short("p")
             .takes_value(true)
-            .help("Number of significant bits to use in an RGB channel"),
+            .help("Number of significant bits to use in an RGB channel. Accepts integer values within the range [1, 8](Default: 6)"),
     );
 
     let app = app.arg(
         Arg::with_name("gradient_step")
             .long("gradient_step")
             .short("g")
             .takes_value(true)
-            .help("Color difference between gradient layers"),
+            .help("Color difference between gradient layers. Accepts integer values within the range [0, 255](Default: 16)"),
     );
 
     let app = app.arg(
         Arg::with_name("corner_threshold")
             .long("corner_threshold")
             .short("c")
             .takes_value(true)
-            .help("Minimum momentary angle (degree) to be considered a corner"),
+            .help("Minimum momentary angle (degree) to be considered a corner. Accepts integer values within the range [0, 180](Default: 60)"),
     );
 
     let app = app.arg(Arg::with_name("segment_length")
         .long("segment_length")
         .short("l")
         .takes_value(true)
-        .help("Perform iterative subdivide smooth until all segments are shorter than this length"));
+        .help("Perform iterative subdivide smooth until all segments are shorter than this length. Accepts values within the range [3.5, 10](Default: 4.0)"));
 
     let app = app.arg(
         Arg::with_name("splice_threshold")
             .long("splice_threshold")
             .short("s")
             .takes_value(true)
-            .help("Minimum angle displacement (degree) to splice a spline"),
+            .help("Minimum angle displacement (degree) to splice a spline. Accepts integer values within the range [0, 180](Default: 45)"),
     );
 
     let app = app.arg(