Create expression struct and memory pool

lib/memory_pool.c

@@ -0,0 +1,15 @@
+#include "memory_pool.h"
+
+#include <stddef.h>
+
+void init_memory_pool(memory_pool_t *pool)
+{
+	pool->free_pointer = &pool->buffer[0];
+}
+
+expression_t *allocate_expression(memory_pool_t *pool)
+{
+	if (pool->free_pointer > pool->buffer + MEMORY_POOL_SIZE)
+		return NULL;
+	return pool->free_pointer++;
+}