Invert stable/unstable features

Closes #1
diff --git a/Cargo.toml b/Cargo.toml
index 9efce2a..44cb9d7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,9 +7,8 @@
 doctest = false
 
 [dependencies]
-synom = { version = "0.11", optional = true }
-unicode-xid = { version = "0.0.4", optional = true }
+synom = "0.11"
+unicode-xid = "0.0.4"
 
 [features]
-stable = ["synom", "unicode-xid"]
-default = ["stable"]
+unstable = []
diff --git a/src/lib.rs b/src/lib.rs
index e1305eb..e0733f7 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,7 +1,7 @@
 extern crate proc_macro;
 
 #[macro_use]
-#[cfg(feature = "stable")]
+#[cfg(not(feature = "unstable"))]
 extern crate synom;
 
 use std::fmt;
@@ -10,10 +10,10 @@
 use std::iter::FromIterator;
 
 #[path = "stable.rs"]
-#[cfg(feature = "stable")]
+#[cfg(not(feature = "unstable"))]
 mod imp;
 #[path = "unstable.rs"]
-#[cfg(not(feature = "stable"))]
+#[cfg(feature = "unstable")]
 mod imp;
 
 #[derive(Clone)]