Added LFS_INFO, upgraded most LFS_DEBUG statements

This adds LFS_INFO and limits LFS_DEBUG to opt-in debug output.

Note that while LFS_DEBUG seems to be only used in LFS_DEBUGRBYDBALANCE,
it can also be useful for adding additional logging while debugging.

Having separate levels here is useful for filtering. Users should be
able to expect LFS_INFO output to not bog down a system, while LFS_DEBUG
can be a free-for-all dumping ground of debug info.

This also converges to the common 4 levels of logging found in other
systems, which was an intentional non-goal, but it's interesting to see
how each level serves a purpose.

lfs_util.h

@@ -35,6 +35,7 @@
 #include <assert.h>
 #endif
 #if !defined(LFS_NO_DEBUG) || \
+        !defined(LFS_NO_INFO) || \
         !defined(LFS_NO_WARN) || \
         !defined(LFS_NO_ERROR) || \
         defined(LFS_YES_TRACE)
@@ -72,6 +73,16 @@ extern "C"
 #endif
 #endif
 
+#ifndef LFS_INFO
+#ifndef LFS_NO_INFO
+#define LFS_INFO_(fmt, ...) \
+    printf("%s:%d:info: " fmt "%s\n", __FILE__, __LINE__, __VA_ARGS__)
+#define LFS_INFO(...) LFS_INFO_(__VA_ARGS__, "")
+#else
+#define LFS_INFO(...)
+#endif
+#endif
+
 #ifndef LFS_WARN
 #ifndef LFS_NO_WARN
 #define LFS_WARN_(fmt, ...) \