Add compression level

Author: marcosc90

src/common.rs

@@ -325,6 +325,8 @@ pub enum Compression {
         note = "use one of the other compression levels instead, such as 'fast'"
     )]
     Rle,
+    /// Integer representing the compression level, typically on a scale of 0-9
+    Level(u32),
 }
 
 impl Default for Compression {

src/encoder.rs

@@ -1702,6 +1702,7 @@ impl Compression {
             Compression::Default => flate2::Compression::default(),
             Compression::Fast => flate2::Compression::fast(),
             Compression::Best => flate2::Compression::best(),
+            Compression::Level(level) => flate2::Compression::new(level),
             #[allow(deprecated)]
             Compression::Huffman => flate2::Compression::none(),
             #[allow(deprecated)]