relaunch ontop of latest grbl edge

code very messy but tested

sim/planner_inject_accessors.c

@@ -0,0 +1,10 @@
+#include "../planner.h"
+
+static block_t block_buffer[BLOCK_BUFFER_SIZE];  // A ring buffer for motion instructions
+block_t *get_block_buffer() { return block_buffer; }
+
+static volatile uint8_t block_buffer_head;       // Index of the next block to be pushed
+uint8_t get_block_buffer_head() { return block_buffer_head; }
+
+static volatile uint8_t block_buffer_tail;       // Index of the next block to be pushed
+uint8_t get_block_buffer_tail() { return block_buffer_tail; }