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/

test/data/test_comment_02.json

@@ -0,0 +1,16 @@
+{
+   /* C-style comment
+
+    C-style-2 comment */
+   "c-test" : {
+      "a" : 1,
+      /* Internal comment c-style */
+      "b" : 2
+   },
+   // C++-style comment
+   "cpp-test" : {
+      // Internal comment cpp-style
+      "c" : 3,
+      "d" : 4
+   }
+}