Simplify char_t and remove msvc2013 from CI

doc/index.rst

@@ -175,8 +175,9 @@ The library is highly portable and relies only on a small set of C++11 features:
 * decltype
 * trailing return types
 * deleted functions
+* alias templates
 
-These are available since GCC 4.4, Clang 2.9 and MSVC 18.0 (2013). For older
+These are available since GCC 4.8, Clang 3.0 and MSVC 19.0 (2015). For older
 compilers use fmt `version 4.x
 <https://github.com/fmtlib/fmt/releases/tag/4.1.0>`_ which continues to be
 maintained and only requires C++98.

include/fmt/core.h

@@ -1306,16 +1306,9 @@ struct wformat_args : basic_format_args<wformat_context> {
       : basic_format_args<wformat_context>(std::forward<Args>(arg)...) {}
 };
 
-#ifndef FMT_USE_ALIAS_TEMPLATES
-#  define FMT_USE_ALIAS_TEMPLATES FMT_HAS_FEATURE(cxx_alias_templates)
-#endif
-#if FMT_USE_ALIAS_TEMPLATES
 /** String's character type. */
 template <typename S> using char_t = typename internal::char_t<S>::type;
-#  define FMT_CHAR(S) fmt::char_t<S>
+#define FMT_CHAR(S) fmt::char_t<S>
-#else
-#  define FMT_CHAR(S) typename internal::char_t<S>::type
-#endif
 
 namespace internal {
 template <typename Context>

support/appveyor.yml

@@ -9,7 +9,6 @@ platform:
   - x64
 
 image:
-  - Visual Studio 2013
   - Visual Studio 2015
   - Visual Studio 2017