Serde and rayon behind feature flags.

src/.#serde.rs

@@ -0,0 +1 @@
+olsson@mr-krusty.local.98510

src/lib.rs

@@ -1,5 +1,7 @@
 extern crate hashbrown;
+#[cfg(feature="rayon")]
 extern crate rayon;
+#[cfg(feature="serde")]
 extern crate serde;
 extern crate unreachable;
 
@@ -9,10 +11,14 @@ use std::iter::{FromIterator, IntoIterator, Iterator};
 use std::ops;
 
 use hashbrown::HashMap;
+#[cfg(feature="rayon")]
 use rayon::iter::{FromParallelIterator, IntoParallelIterator, ParallelExtend, ParallelIterator};
-use serde::de::{SeqAccess, Visitor};
-use serde::ser::SerializeSeq;
-use serde::{Deserialize, Deserializer, Serialize, Serializer};
+#[cfg(feature="serde")]
+use serde::{
+    {Deserialize, Deserializer, Serialize, Serializer},
+    de::{SeqAccess, Visitor},
+    ser::SerializeSeq,
+};
 
 const BITS: u64 = 64;
 
@@ -376,6 +382,7 @@ impl Iterator for IntoIter {
     }
 }
 
+#[cfg(feature="rayon")]
 impl ParallelExtend<u64> for BitSet {
     fn par_extend<I>(&mut self, par_iter: I)
     where
@@ -399,6 +406,7 @@ impl ParallelExtend<u64> for BitSet {
     }
 }
 
+#[cfg(feature="rayon")]
 impl FromParallelIterator<u64> for BitSet {
     fn from_par_iter<I>(par_iter: I) -> Self
     where
@@ -410,6 +418,7 @@ impl FromParallelIterator<u64> for BitSet {
     }
 }
 
+#[cfg(feature="serde")]
 impl Serialize for BitSet {
     #[inline]
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
@@ -424,6 +433,7 @@ impl Serialize for BitSet {
     }
 }
 
+#[cfg(feature="serde")]
 impl<'de> Deserialize<'de> for BitSet {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where