Fix conversion warnings/errors

See #411.
  http://paste.debian.net/378673/

include/json/reader.h

@@ -42,8 +42,8 @@ public:
    *
    */
   struct StructuredError {
-    size_t offset_start;
-    size_t offset_limit;
+    ptrdiff_t offset_start;
+    ptrdiff_t offset_limit;
     std::string message;
   };
 

include/json/value.h

@@ -554,10 +554,10 @@ Json::Value obj_value(Json::objectValue); // {}
 
   // Accessors for the [start, limit) range of bytes within the JSON text from
   // which this value was parsed, if any.
-  void setOffsetStart(size_t start);
-  void setOffsetLimit(size_t limit);
-  size_t getOffsetStart() const;
-  size_t getOffsetLimit() const;
+  void setOffsetStart(ptrdiff_t start);
+  void setOffsetLimit(ptrdiff_t limit);
+  ptrdiff_t getOffsetStart() const;
+  ptrdiff_t getOffsetLimit() const;
 
 private:
   void initBasic(ValueType type, bool allocated = false);
@@ -598,8 +598,8 @@ private:
 
   // [start, limit) byte offsets in the source JSON text from which this Value
   // was extracted.
-  size_t start_;
-  size_t limit_;
+  ptrdiff_t start_;
+  ptrdiff_t limit_;
 };
 
 /** \brief Experimental and untested: represents an element of the "path" to

include/json/writer.h

@@ -238,8 +238,8 @@ private:
   ChildValues childValues_;
   std::string document_;
   std::string indentString_;
-  int rightMargin_;
-  int indentSize_;
+  unsigned int rightMargin_;
+  unsigned int indentSize_;
   bool addChildValues_;
 };