Add .editorconfig, .gitignore and FFmpeg deprecation note

.editorconfig

@@ -0,0 +1,9 @@
+root = true
+
+[*]
+indent_style             = tab
+indent_size              = 4
+charset                  = utf-8
+end_of_line              = lf
+trim_trailing_whitespace = true
+insert_final_newline     = true

.gitignore

@@ -0,0 +1,6 @@
+desktop.ini
+.DS_Store
+.vscode/
+build/
+.cache/
+*.code-workspace

psxavenc/decoding.c

@@ -399,6 +399,7 @@ void close_av_data(settings_t *settings)
 
 	av_frame_free(&(av->frame));
 	swr_free(&(av->resampler));
+	// Deprecated, kept for compatibility with older FFmpeg versions.
 	avcodec_close(av->audio_codec_context);
 	avcodec_free_context(&(av->audio_codec_context));
 	avformat_free_context(av->format);