Sending end of the wallet

Most of the logic to build a transaction that sends coin to
another party. Still requires more debugging and clean up.
Main changes and additions are:

* Update to serde 1.0
* API endpoint to retrieve an Output
* Output is now Serialize and Deserialize
* Wallet configuration
* Command line for the send operation
* Wallet data checker to update created outputs into confirmed
* Wallet-specific configuration

core/src/core/hash.rs

@@ -17,6 +17,7 @@
 //! Primary hash function used in the protocol
 //!
 
+use std::cmp::min;
 use std::{fmt, ops};
 use tiny_keccak::Keccak;
 use std::convert::AsRef;
@@ -47,6 +48,16 @@ impl fmt::Display for Hash {
 }
 
 impl Hash {
+  /// Builds a Hash from a byte vector. If the vector is too short, it will be
+  /// completed by zeroes. If it's too long, it will be truncated.
+  pub fn from_vec(v: Vec<u8>) -> Hash {
+    let mut h = [0; 32];
+    for i in 0..min(v.len(), 32) {
+      h[i] = v[i];
+    }
+    Hash(h)
+  }
+
 	/// Converts the hash to a byte vector
 	pub fn to_vec(&self) -> Vec<u8> {
 		self.0.to_vec()

core/src/core/target.rs

@@ -105,9 +105,9 @@ impl Serialize for Difficulty {
 	}
 }
 
-impl Deserialize for Difficulty {
+impl<'de> Deserialize<'de> for Difficulty {
 	fn deserialize<D>(deserializer: D) -> Result<Difficulty, D::Error>
-		where D: Deserializer
+		where D: Deserializer<'de>
 	{
 		deserializer.deserialize_i32(DiffVisitor)
 	}
@@ -115,7 +115,7 @@ impl Deserialize for Difficulty {
 
 struct DiffVisitor;
 
-impl de::Visitor for DiffVisitor {
+impl<'de> de::Visitor<'de> for DiffVisitor {
 	type Value = Difficulty;
 
 	fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {

core/src/core/transaction.rs

@@ -269,6 +269,7 @@ impl Input {
 
 bitflags! {
     /// Options for block validation
+    #[derive(Serialize, Deserialize)]
     pub flags OutputFeatures: u8 {
         /// No flags
         const DEFAULT_OUTPUT = 0b00000000,
@@ -279,10 +280,9 @@ bitflags! {
 
 /// Output for a transaction, defining the new ownership of coins that are being
 /// transferred. The commitment is a blinded value for the output while the
-/// range
-/// proof guarantees the commitment includes a positive value without overflow
-/// and the ownership of the private key.
-#[derive(Debug, Copy, Clone, PartialEq)]
+/// range proof guarantees the commitment includes a positive value without
+/// overflow and the ownership of the private key.
+#[derive(Debug, Copy, Clone, PartialEq, Serialize, Deserialize)]
 pub struct Output {
 	/// Options for an output's structure or use
 	pub features: OutputFeatures,