spi.hpp: Add C++ wrapper around Spi

* maa_spi_context becomes an opaque pointer
* C++ wrapper class Spi created
* swig now uses C++ wrapper Gpio to generate API

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

examples/spi_mcp4261.c

@@ -30,10 +30,10 @@ int
 main(int argc, char **argv)
 {
     maa_init();
-    maa_spi_context *spi;
+    maa_spi_context spi;
     spi = maa_spi_init(0);
     unsigned int response = 0;
-    printf("Hello, SPI initialised: fd=%i\n",spi->spifd);
+    printf("Hello, SPI initialised\n");
     uint8_t data[] = {0x00, 100};
     uint8_t *recv;
     while(1) {