Show (short) list of possible enum values when an invalid value is encountered (resolves #1318)

All enum errors have (hopefully) been changed to a luax_enumerror, which has a
fixed error message. If additionally a list of valid options is passed, it
lists that in the error message. For every enum error with few options I've
implemented this using a getConstants call.

This solution has been designed specifically to reduce the number of template
instantiations (as I've been told that was a concern). All new template code
happens in places where there already was an instantiation of the relevant
StringMap. Of course there is still std::vector<std::string>...

--HG--
branch : minor

src/common/StringMap.h

@@ -23,6 +23,9 @@
 
 #include "Exception.h"
 
+#include <string>
+#include <vector>
+
 namespace love
 {
 
@@ -145,6 +148,18 @@ public:
 		return hash;
 	}
 
+	std::vector<std::string> getNames() const
+	{
+		std::vector<std::string> names;
+		names.reserve(SIZE);
+
+		for (unsigned int i = 0; i < SIZE; ++i)
+			if (reverse[i] != nullptr)
+				names.emplace_back(reverse[i]);
+
+		return names;
+	}
+
 private:
 
 	struct Record