Remove compatability with CMake <=3.19 (refs #114)

Author: scheibel

README.md

@@ -21,7 +21,7 @@ The main target platforms are typical desktop, laptop, and server platforms. Cur
 However, other UNIX versions may work as well if they are supported by CMake.
 
 The cmake-init template assumes you want to setup a project using
-* CMake (3.15 or above)
+* CMake (3.20 or above)
 * C/C++ compiler
 
 
@@ -99,7 +99,7 @@ As with most CMake projects, cmake-init initializes the CMake environment. This
 
 ```cmake
 # CMake version
-cmake_minimum_required(VERSION 3.15 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.20 FATAL_ERROR)
 ```
 
 required policies,

source/baselib/CMakeLists.txt

@@ -73,7 +73,7 @@ write_compiler_detection_header(
     PREFIX ${target_id}
     COMPILERS AppleClang Clang GNU MSVC
     FEATURES cxx_alignas cxx_alignof cxx_constexpr cxx_final cxx_noexcept cxx_nullptr cxx_sizeof_member cxx_thread_local
-    VERSION 3.15
+    VERSION 3.20
 )
 
 # Create API export header

source/fiblib/CMakeLists.txt

@@ -75,7 +75,7 @@ write_compiler_detection_header(
     PREFIX ${target_id}
     COMPILERS AppleClang Clang GNU MSVC
     FEATURES cxx_alignas cxx_alignof cxx_constexpr cxx_final cxx_noexcept cxx_nullptr cxx_sizeof_member cxx_thread_local
-    VERSION 3.15
+    VERSION 3.20
 )
 
 # Create API export header

source/tests/CMakeLists.txt

@@ -4,7 +4,7 @@
 #
 
 # CMake version
-cmake_minimum_required(VERSION 3.15 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.20 FATAL_ERROR)
 
 # Meta information about the project
 set(META_PROJECT_NAME "template")