Add "bitcoin-tx" command line utility and supporting modules.

This is a simple utility that provides command line manipulation of
a hex-encoded TX. The utility takes a hex string on the command line
as input, performs zero or more mutations, and outputs a hex string
to standard output.

This utility is also an intentional exercise of the "bitcoin library"
concept. It is designed to require minimal libraries, and works
entirely without need for any RPC or P2P communication.

See "bitcoin-tx --help" for command and options summary.

src/core_read.cpp

@@ -4,12 +4,14 @@
 #include "core.h"
 #include "serialize.h"
 #include "script.h"
+#include "util.h"
 
 #include <boost/assign/list_of.hpp>
 #include <boost/algorithm/string/classification.hpp>
 #include <boost/algorithm/string/predicate.hpp>
 #include <boost/algorithm/string/split.hpp>
 #include <boost/algorithm/string/replace.hpp>
+#include "univalue/univalue.h"
 
 using namespace std;
 using namespace boost;
@@ -100,3 +102,26 @@ bool DecodeHexTx(CTransaction& tx, const std::string& strHexTx)
     return true;
 }
 
+uint256 ParseHashUV(const UniValue& v, const string& strName)
+{
+    string strHex;
+    if (v.isStr())
+        strHex = v.getValStr();
+    if (!IsHex(strHex)) // Note: IsHex("") is false
+        throw runtime_error(strName+" must be hexadecimal string (not '"+strHex+"')");
+
+    uint256 result;
+    result.SetHex(strHex);
+    return result;
+}
+
+vector<unsigned char> ParseHexUV(const UniValue& v, const string& strName)
+{
+    string strHex;
+    if (v.isStr())
+        strHex = v.getValStr();
+    if (!IsHex(strHex))
+        throw runtime_error(strName+" must be hexadecimal string (not '"+strHex+"')");
+    return ParseHex(strHex);
+}
+