Revert "Merge pull request #47 from lioncash/remove-stringfromint"

Breaks Android build.

This reverts commit 12d026c544, reversing
changes made to 6d678490f5.

Source/Core/Common/StringUtil.h

@@ -55,6 +55,7 @@ std::string ThousandSeparate(I value, int spaces = 0)
 	return oss.str();
 }
 
+std::string StringFromInt(int value);
 std::string StringFromBool(bool value);
 
 bool TryParse(const std::string &str, bool *output);