Added signal handlers (and placeholder for SEH handlers)

- based on PR 232 (https://github.com/philsquared/Catch/pull/232 - thanks Lukasz Forynski)
- Writes to reporter, so gets all the usual context, but then exits directly (since the stack cannot be resumed) so no summary
- On Windows does nothing, as yet.

projects/SelfTest/MiscTests.cpp

@@ -380,3 +380,9 @@ TEST_CASE( "toString on wchar_t returns the string contents", "[toString]" ) {
 	std::string result = Catch::toString( s );
 	CHECK( result == "\"wide load\"" );
 }
+
+TEST_CASE( "Divide by Zero signal handler", "[.][sig]" ) {
+    int i = 0;
+    int x = 10/i; // This should cause the signal to fire
+    CHECK( x == 0 );
+}