exception: Add exceptions when context creation fails

* Exceptions only fired in constructor when it would initialise with a NULL
  context causing segfaults if used any further
* Adds exception.i requirement to mraa.i for node.js and python support

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

src/mraa.i

@@ -1,5 +1,6 @@
 %include stdint.i
 %include std_string.i
+%include exception.i
 
 #ifdef DOXYGEN
     %include common_hpp_doc.i
@@ -26,6 +27,16 @@
     mraa_init();
 %}
 
+%exception {
+    try {
+        $action
+    } catch(const std::invalid_argument& e) {
+        SWIG_exception(SWIG_ValueError, e.what());
+    } catch(...) {
+        SWIG_exception(SWIG_RuntimeError, "Unknown exception");
+    }
+}
+
 %typemap(in) uint8_t = char;
 %typemap(in) unsigned char* = char*;
 %apply (char *STRING, size_t LENGTH) { (char *data, size_t length) };