Create a CMakeLists.txt file and create an interface library

Also move exprtk.hpp into an include folder

CMakeLists.txt

@@ -0,0 +1,42 @@
+# **************************************************************
+# *         C++ Mathematical Expression Toolkit Library        *
+# *                                                            *
+# * Author: Arash Partow (1999-2023)                           *
+# * URL: https://www.partow.net/programming/exprtk/index.html  *
+# *                                                            *
+# * Copyright notice:                                          *
+# * Free use of the Mathematical Expression Toolkit Library is *
+# * permitted under the guidelines and in accordance with the  *
+# * most current version of the MIT License.                   *
+# * http://www.opensource.org/licenses/MIT                     *
+# *                                                            *
+# **************************************************************
+
+# set the minimum version of cmake required
+cmake_minimum_required(VERSION 3.14)
+
+# set the project name
+project(ExprTk)
+
+# specify the C++ standard
+set(CMAKE_CXX_STANDARD 11)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+# set additional compiler flags
+set(CMAKE_VERBOSE_MAKEFILE ON)
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+
+# Appends the cmake path to MAKE_MODULE_PATH variable.
+set(CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake ${CMAKE_MODULE_PATH})
+
+# Determine ExprTk Source Version
+find_package(Git QUIET)
+include(GitDetermineVersion)
+# The upcoming command sets the following variables: ExprTk_VERSION, ExprTk_VERSION_MAJOR, ExprTk_VERSION_MINOR,
+# ExprTk_VERSION_PATCH, ExprTk_VERSION_PATCH_EXTRA, ExprTk_VERSION_FULL
+determine_version("${CMAKE_CURRENT_SOURCE_DIR}" "${GIT_EXECUTABLE}" "ExprTk")
+
+# create an interface library for the ExprTk header
+add_library(ExprTk INTERFACE)
+# set the include directory for the interface library
+target_include_directories(ExprTk INTERFACE include)