Add pio onewire example (#334)

* Adds PIO onewire example

Co-authored-by: martin <admin@crossleys.biz>

pio/onewire/onewire_library/onewire_library.h

@@ -0,0 +1,17 @@
+#include "hardware/pio.h"
+#include "hardware/clocks.h"            // for clock_get_hz() in generated header
+#include "onewire_library.pio.h"        // generated by pioasm
+
+typedef struct {
+    PIO pio;
+    uint sm;
+    uint jmp_reset;
+    int offset;
+    int gpio;
+} OW;
+
+bool ow_init (OW *ow, PIO pio, uint offset, uint gpio);
+void ow_send (OW *ow, uint data);
+uint8_t ow_read (OW *ow);
+bool ow_reset (OW *ow);
+int ow_romsearch (OW *ow, uint64_t *romcodes, int maxdevs, uint command);