Simplify header includes

This makes some stuff have redundant includes, but we'll worry about
that more later when we actually have a lot of files.

base.h

@@ -1,5 +1,11 @@
 #pragma once
+#include <assert.h>
+#include <limits.h>
+#include <ncurses.h>
+#include <stdbool.h>
 #include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
 
 typedef char Term;
 typedef uint32_t U32;

field.c

@@ -1,8 +1,4 @@
 #include "field.h"
-#include <assert.h>
-#include <ncurses.h>
-#include <stdlib.h>
-#include <string.h>
 
 void field_init_zeros(Field* f, U32 height, U32 width) {
   size_t num_cells = height * width;

main.c

@@ -1,12 +1,6 @@
 #include "base.h"
 #include "field.h"
-#include <assert.h>
-#include <limits.h>
 #include <locale.h>
-#include <ncurses.h>
-#include <stdbool.h>
-#include <stdlib.h>
-#include <string.h>
 #include <unistd.h>
 
 int main() {