Rename 'Standard Gaming Platform' to 'sgp' (#246)

* rename 'Standard Gaming Platform' to 'sgp'

* Adapt CMakeLists.txt files to renamed SGP directory

* Lowercase it

sgp/stringicmp.h

@@ -0,0 +1,16 @@
+//
+// Snap: Declaration of case-insensitive string comparison classes
+//
+#pragma warning(disable:4786)
+#ifndef STRINGICMP_H
+#define STRINGICMP_H
+
+#include <string>
+
+// Function-object that compares strings (s1 < s2) ignoring case
+class TStringiLess {
+public:
+	bool operator() (std::string const& s1, std::string const& s2) const;
+};
+
+#endif // STRINGICMP_H