Support mode that doesn't override defaults

Fixes #4

src/lib.rs

@@ -204,11 +204,17 @@ macro_rules! big_array {
             }
         )+
     };
-    ($name:ident;) => {
+    ($name:ident; + $($len:expr,)*) => {
         big_array! {
             $name;
             40, 48, 50, 56, 64, 72, 96, 100, 128, 160, 192, 200, 224, 256, 384, 512,
             768, 1024, 2048, 4096, 8192, 16384, 32768, 65536,
+            $($len,)*
+        }
+    };
+    ($name:ident;) => {
+        big_array! {
+            $name; +
         }
     }
 }

tests/plus.rs

@@ -0,0 +1,27 @@
+#![no_std]
+
+extern crate serde;
+#[macro_use]
+extern crate serde_derive;
+extern crate serde_json;
+#[macro_use]
+extern crate serde_big_array;
+
+big_array! { BigArray; +127, }
+
+#[derive(Serialize, Deserialize)]
+struct S {
+    #[serde(with = "BigArray")]
+    arr: [u8; 64],
+    #[serde(with = "BigArray")]
+    arr_2: [u8; 127],
+}
+
+#[test]
+fn test() {
+    let s = S { arr: [1; 64], arr_2: [1; 127] };
+    let j = serde_json::to_string(&s).unwrap();
+    let s_back = serde_json::from_str::<S>(&j).unwrap();
+    assert!(&s.arr[..] == &s_back.arr[..]);
+    assert!(&s.arr_2[..] == &s_back.arr_2[..]);
+}