remove rustc-serialize feature and bump version (#22)

* remove rustc-serialize

* bump version to 0.6.0

* remove bincode

src/fields/fp.rs

@@ -4,9 +4,6 @@ use rand::Rng;
 use crate::fields::FieldElement;
 use crate::arith::{U256, U512};
 
-#[cfg(feature = "rustc-serialize")]
-use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
-
 macro_rules! field_impl {
     ($name:ident, $modulus:expr, $rsquared:expr, $rcubed:expr, $one:expr, $inv:expr) => {
         #[derive(Copy, Clone, PartialEq, Eq, Debug)]
@@ -22,22 +19,6 @@ macro_rules! field_impl {
             }
         }
 
-        #[cfg(feature = "rustc-serialize")]
-        impl Encodable for $name {
-            fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
-                let normalized = U256::from(*self);
-
-                normalized.encode(s)
-            }
-        }
-
-        #[cfg(feature = "rustc-serialize")]
-        impl Decodable for $name {
-            fn decode<S: Decoder>(s: &mut S) -> Result<$name, S::Error> {
-                $name::new(U256::decode(s)?).ok_or_else(|| s.error("integer is not less than modulus"))
-            }
-        }
-
         impl $name {
             pub fn from_str(s: &str) -> Option<Self> {
                 let ints: Vec<_> = {
@@ -240,7 +221,7 @@ field_impl!(
     0x9ede7d651eca6ac987d20782e4866389
 );
 
-lazy_static! {
+lazy_static::lazy_static! {
 
     static ref FQ: U256 = U256::from([
         0x3c208c16d87cfd47,