let all utf8/wide functions can be available just by including utf8/utf8.h

while here:
- remove utf8/utf8_stream.h, now we only need utf8/utf8.h to include
- add some new methods for converting from a utf8 stream to wide stream/string
- do some improvements in TextStream:
  - don't use temporary objects to convert utf8/wide
  - add put_stream() which takes TextStreamBase<> as its argument
    (uses an iterator instead of get_char() for reading)
  - let operator<<(const Space & space) serialize to json and not to Space

src/utf8/utf8.cpp

@@ -5,7 +5,7 @@
  */
 
 /* 
- * Copyright (c) 2010-2021, Tomasz Sowa
+ * Copyright (c) 2010-2022, Tomasz Sowa
  * All rights reserved.
  * 
  * Redistribution and use in source and binary forms, with or without
@@ -128,6 +128,25 @@ bool surrogate_pair_to_int(int c1, int c2, int & z)
 
 
 
+/*
+	converts an int to a wide string
+*/
+void int_to_wide(int c, std::wstring & res)
+{
+	if( sizeof(wchar_t)==2 && c>0xffff )
+	{
+		// UTF16 surrogate pairs
+		c -= 0x10000;
+		res += static_cast<wchar_t>(((c >> 10) & 0x3FF) + 0xD800);
+		res += static_cast<wchar_t>((c & 0x3FF) + 0xDC00);
+	}
+	else
+	{
+		res += static_cast<wchar_t>(c);
+	}
+}
+
+
 
 /*!
 	this function converts one UTF-8 character into one wide-character
@@ -312,7 +331,7 @@ unsigned char uz;
 				uz = utf8.get_char(stream_index + i);
 
 				if( !private_namespace::utf8_to_int_add_next_octet(uz, res) )
-					return i;
+					return i + 1;
 			}
 
 			if( utf8_check_range(res, len) )
@@ -330,26 +349,6 @@ unsigned char uz;
 
 
 
-/*
-
-*/
-static void int_to_wide(int c, std::wstring & res)
-{
-	if( sizeof(wchar_t)==2 && c>0xffff )
-	{
-		// UTF16 surrogate pairs
-		c -= 0x10000;
-		res += static_cast<wchar_t>(((c >> 10) & 0x3FF) + 0xD800);
-		res += static_cast<wchar_t>((c & 0x3FF) + 0xDC00);
-	}
-	else
-	{
-		res += static_cast<wchar_t>(c);
-	}
-}
-
-
-
 
 
 /*!