docs: fix compression level range from 0-9 to 0-10

Also store the min, max, and default levels as constants.
While calling `Compression::new`, assert that level is in range.

src/lib.rs

@@ -187,41 +187,46 @@ fn _assert_send_sync() {
 pub struct Compression(u32);
 
 impl Compression {
+    const MAX: u32 = 10;
+    const MIN: u32 = 0;
+    const DEFAULT: u32 = 6;
     /// Creates a new description of the compression level with an explicitly
     /// specified integer.
     ///
-    /// The integer here is typically on a scale of 0-9 where 0 means "no
-    /// compression" and 9 means "take as long as you'd like".
-    pub const fn new(level: u32) -> Compression {
-        Compression(level)
+    /// The integer here is typically on a scale of 0-10 where 0 means "no
+    /// compression" and 10 means "take as long as you'd like".
+    pub fn new(level: u32) -> Self {
+        // Ensure early that the level is within the valid range
+        debug_assert!(level <= Self::MAX);
+        Self(level)
     }
 
     /// No compression is to be performed, this may actually inflate data
     /// slightly when encoding.
-    pub const fn none() -> Compression {
-        Compression(0)
+    pub const fn none() -> Self {
+        Self(Self::MIN)
     }
 
     /// Optimize for the best speed of encoding.
-    pub const fn fast() -> Compression {
-        Compression(1)
+    pub const fn fast() -> Self {
+        Self(1)
     }
 
     /// Optimize for the size of data being encoded.
-    pub const fn best() -> Compression {
-        Compression(9)
+    pub const fn best() -> Self {
+        Self(Self::MAX)
     }
 
     /// Returns an integer representing the compression level, typically on a
-    /// scale of 0-9
+    /// scale of 0-10
     pub fn level(&self) -> u32 {
         self.0
     }
 }
 
 impl Default for Compression {
-    fn default() -> Compression {
-        Compression(6)
+    fn default() -> Self {
+        Self(Self::DEFAULT)
     }
 }