Refactor: improve naming & types

* renamed display traits to Draw*
* renamed Send to SendBits to differentiate from the standard trait
* introduced the Paint trait
* changed type of coordinate to u8 instead of usize
* use generic constant when performing moodulo operation based on screen
  size

src/bit_string/mod.rs

@@ -1,7 +1,7 @@
 mod thumbv6m;
 
-pub trait Sender {
-    fn send(&self, value: u32);
+pub trait SendBits {
+    fn send_bits(&self, value: u32);
 }
 
 pub use thumbv6m::Msb2LsbSender;