Improved documentation for customization (#287)

* move constants to new file, and update documentation

* documentation improvements, deploy checks tests

* fix pylint

* improved code style

* swap build and check

src/ctap/storage/key.rs

@@ -141,7 +141,7 @@ mod test {
 
     #[test]
     fn enough_credentials() {
-        use super::super::MAX_SUPPORTED_RESIDENT_KEYS;
+        use crate::ctap::customization::MAX_SUPPORTED_RESIDENT_KEYS;
         assert!(MAX_SUPPORTED_RESIDENT_KEYS <= CREDENTIALS.end - CREDENTIALS.start);
     }