Constructors and context -> sys

We can register memory we've allocated onto the heap into a ~sys_t~
instance for examination (read: garbage collection) later.  We can
also add items to the symbol table it has internally.

build.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env sh
 
 CFLAGS="-Wall -Wextra -std=c11 -ggdb -fsanitize=address -fsanitize=undefined"
-SRC="vec.c tag.c symtable.c main.c"
+SRC="vec.c symtable.c tag.c constructor.c sys.c main.c"
 OUT="alisp.out"
 
 set -xe