Extract logging logic

Previously logging logic was scattered over OS class implementations
with plenty of duplication. Major changes in this commit:

 - Extracted logging logic into a separate Logger hierarchy. It allows
   easy configuration of logging mechanism depending on compile-time or
   run-time configuration.

 - Implemented RotatedFileLogger which is usually used with StdLogger,
   providing persistency of logs. It is often important to be able to
   obtain logs of the game even in production to be able to understand
   what happened prior to some problem. On mobile there previously was
   no way to obtain the logs aside from having the device connected to
   your machine.

 - flush() is not performed in release mode for every logged line. It
   is only performed for errors.

1 files changed, 1 insertions, 0 deletions

diff --git a/core/io/file_access_pack.h b/core/io/file_access_pack.h
index 3deb0d2bd3..12187a353a 100644
--- a/core/io/file_access_pack.h
+++ b/core/io/file_access_pack.h
@@ -161,6 +161,7 @@ public:
 
 	virtual Error get_error() const;
 
+	virtual void flush();
 	virtual void store_8(uint8_t p_dest);
 
 	virtual void store_buffer(const uint8_t *p_src, int p_length);