use platform-specific NSString for case changes on OS X/iOS

refs #309

common/platform_default.cpp

@@ -0,0 +1,25 @@
+#include <mbgl/platform/platform.hpp>
+
+#include <locale>
+
+namespace mbgl {
+namespace platform {
+
+std::string uppercase(const std::string& string) {
+    // TODO: Use a proper Unicode Special Casing-aware algorithm.
+    const auto &convert = std::use_facet<std::ctype<char>>(std::locale());
+    std::string converted = string;
+    convert.toupper(&converted[0], &converted[0] + converted.size());
+    return converted;
+}
+
+std::string lowercase(const std::string& string) {
+    // TODO: Use a proper Unicode Special Casing-aware algorithm.
+    const auto &convert = std::use_facet<std::ctype<char>>(std::locale());
+    std::string converted = string;
+    convert.tolower(&converted[0], &converted[0] + converted.size());
+    return converted;
+}
+
+}
+}