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/filter.h

@@ -0,0 +1,21 @@
+#ifndef FILTER_H
+#define FILTER_H
+
+#include <vector>
+
+extern "C" {
+#include <libavcodec/avcodec.h>
+#include <libavfilter/avfilter.h>
+#include <libavutil/buffer.h>
+}
+
+// Abstract base class for filters
+class Filter {
+   public:
+    virtual ~Filter() {}
+    virtual int init(AVCodecContext *dec_ctx, AVCodecContext *enc_ctx, AVBufferRef *hw_ctx) = 0;
+    virtual int process_frame(AVFrame *input_frame, AVFrame **output_frame) = 0;
+    virtual int flush(std::vector<AVFrame *> &processed_frames) = 0;
+};
+
+#endif  // FILTER_H