build: remove CPM.cmake file File (#54)

* build: move the simplified content of `cmake/CPM.cmake` to `CMakeLists.txt`

* build: download the `CPM.cmake` inside `_deps` directory instead

Author: threeal

CMakeLists.txt

@@ -2,7 +2,10 @@ cmake_minimum_required(VERSION 3.0)
 
 project(example)
 
-include(cmake/CPM.cmake)
+file(DOWNLOAD https://github.com/cpm-cmake/CPM.cmake/releases/download/v0.38.6/CPM.cmake
+     ${CMAKE_BINARY_DIR}/_deps/CPM.cmake
+     EXPECTED_HASH SHA256=11c3fa5f1ba14f15d31c2fb63dbc8628ee133d81c8d764caad9a8db9e0bacb07)
+include(${CMAKE_BINARY_DIR}/_deps/CPM.cmake)
 cpmusepackagelock(package-lock)
 
 cpmgetpackage(CheckWarning.cmake)