Add basic main CLI

I'm a visual type of person, I like to watch things evolve on the
command line. So I've added a basic main.rs to the project to watch
things on the command line as they evolve.

src/board.rs

@@ -1,14 +1,32 @@
 use crate::cell::{Cell, CellValue};
 use std::collections::HashSet;
+use std::fmt;
 use ndarray::prelude::*;
 
 const REGION_SIZE: usize = 9;
 const SUB_REGION_SIZE: usize = 3;
 
+#[derive(Debug)]
 pub struct Board {
     cells: Array2<Cell>,
 }
 
+impl fmt::Display for Board {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        let mut str = String::from("");
+        for row in self.cells.outer_iter() {
+            for cell in row.iter() {
+                match cell.value() {
+                    Some(s) => str += &s.to_string(),
+                    None => str += "?",
+                }
+            }
+            str += "\n";
+        }
+        fmt.write_str(&str)
+    }
+}
+
 impl Board {
     pub fn new() -> Board {
         let cells = Array2::zeros((REGION_SIZE, REGION_SIZE));
@@ -65,6 +83,12 @@ pub struct Point {
 }
 
 impl Point {
+    pub fn new(row: usize, col: usize) -> Point {
+        Point {
+            row, col
+        }
+    }
+
     fn coordinates(&self) -> [usize; 2] {
         [self.row, self.col]
     }

src/cell.rs

@@ -1,6 +1,7 @@
 use std::collections::HashSet;
 use num_traits::identities::Zero;
 use std::ops::Add;
+use std::string::ToString;
 
 #[derive(Clone, Debug, Copy, Hash, Eq, PartialEq)]
 pub enum CellValue {
@@ -15,6 +16,22 @@ pub enum CellValue {
     Nine,
 }
 
+impl ToString for CellValue {
+    fn to_string(&self) -> String {
+        match self {
+            CellValue::One => String::from("1"),
+            CellValue::Two => String::from("2"),
+            CellValue::Three => String::from("3"),
+            CellValue::Four => String::from("4"),
+            CellValue::Five => String::from("5"),
+            CellValue::Six => String::from("6"),
+            CellValue::Seven => String::from("7"),
+            CellValue::Eight => String::from("8"),
+            CellValue::Nine => String::from("9")
+        }
+    }
+}
+
 #[derive(Clone, Debug)]
 pub struct Cell {
     value: Option<CellValue>,

src/lib.rs

@@ -1,2 +1,6 @@
-pub mod cell;
+mod cell;
-pub mod board;
+mod board;
+
+pub use board::Board;
+pub use board::Point;
+pub use cell::CellValue;

src/main.rs

@@ -0,0 +1,10 @@
+use rustdoku::Board;
+use rustdoku::CellValue;
+use rustdoku::Point;
+
+fn main() {
+    let mut board = Board::new();
+
+    board.set_value(&Point::new(1, 2), CellValue::One);
+    println!("{}", board);
+}