feat(*): switched to spdlog for logging and organized headers (#1183)

* feat: updated PKGBUILD description
* feat: updated workflow syntax and dependencies
* feat: switched logging to spdlog
* chore: adjusted library defaults
* ci: fixed spdlog format string issues
* docs: fixed docs for libvideo2x functions
* feat: organized header files
* fix: fixed header installation directory
* feat: link spdlog statically if compiled from source
* feat: adjusted libvideo2x log level enum names
* feat: added version.h header

Signed-off-by: k4yt3x <i@k4yt3x.com>

include/libvideo2x/decoder.h

@@ -0,0 +1,18 @@
+#ifndef DECODER_H
+#define DECODER_H
+
+extern "C" {
+#include <libavcodec/avcodec.h>
+#include <libavformat/avformat.h>
+}
+
+int init_decoder(
+    AVHWDeviceType hw_type,
+    AVBufferRef *hw_ctx,
+    const char *input_filename,
+    AVFormatContext **fmt_ctx,
+    AVCodecContext **dec_ctx,
+    int *video_stream_index
+);
+
+#endif  // DECODER_H