Move implementation files into their own folder

main.c and test.c generate binary executables so they can stay in the
main folder, but the rest can go into their own dedicated folder to
make it look nicer

sv.c

@@ -1,27 +0,0 @@
-/* Copyright (C) 2025 Aryadev Chavali
-
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the Unlicense
- * for details.
-
- * You may distribute and modify this code under the terms of the
- * Unlicense, which you should have received a copy of along with this
- * program.  If not, please go to <https://unlicense.org/>.
-
- * Created: 2025-08-21
- * Description: String views
- */
-
-#include <malloc.h>
-#include <string.h>
-
-#include "./alisp.h"
-
-sv_t sv_copy(sv_t old)
-{
-  char *newstr = calloc(1, (old.size + 1) * sizeof(*newstr));
-  memcpy(newstr, old.data, old.size);
-  newstr[old.size] = '\0';
-  return SV(newstr, old.size);
-}