Refactor nvfbc into abstract capture api

src/capture/capture.c

@@ -0,0 +1,17 @@
+#include "../../include/capture/capture.h"
+
+int gsr_capture_start(gsr_capture *cap) {
+    return cap->start(cap);
+}
+
+void gsr_capture_stop(gsr_capture *cap) {
+    cap->stop(cap);
+}
+
+int gsr_capture_capture(gsr_capture *cap, AVFrame *frame) {
+    return cap->capture(cap, frame);
+}
+
+void gsr_capture_destroy(gsr_capture *cap) {
+    cap->destroy(cap);
+}