Comment reading/write improvements

This patch fixes some aspects of reading and writing comments:
- Multiple C++-style comments before a Json value had extra newlines appended to them. This patch removes the addition of those newlines.
- Comments written before Json values in the StyledWriter were not indented to match the indentation level of the value. This patch adds indentation to comments.
- Fixed inconsistency in newlines following C- and C++-style comments being saved as part of the comment. All newlines at the end of a comment are now removed.
- Added an additional test of comments.

https://sourceforge.net/p/jsoncpp/patches/25/

src/lib_json/json_reader.cpp

@@ -191,6 +191,17 @@ Reader::readValue()
 
    if ( collectComments_  &&  !commentsBefore_.empty() )
    {
+      // Remove newline characters at the end of the comments
+      size_t lastNonNewline = commentsBefore_.find_last_not_of("\r\n");
+      if (lastNonNewline != std::string::npos)
+      {
+         commentsBefore_.erase(lastNonNewline+1);
+      }
+      else
+      {
+         commentsBefore_.clear();
+      }
+
       currentValue().setComment( commentsBefore_, commentBefore );
       commentsBefore_ = "";
    }