Run cmake-init and setup flake.nix and default.nix

cmake/spell.cmake

@@ -0,0 +1,29 @@
+cmake_minimum_required(VERSION 3.14)
+
+macro(default name)
+  if(NOT DEFINED "${name}")
+    set("${name}" "${ARGN}")
+  endif()
+endmacro()
+
+default(SPELL_COMMAND codespell)
+default(FIX NO)
+
+set(flag "")
+if(FIX)
+  set(flag -w)
+endif()
+
+execute_process(
+    COMMAND "${SPELL_COMMAND}" ${flag}
+    WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}"
+    RESULT_VARIABLE result
+)
+
+if(result EQUAL "65")
+  message(FATAL_ERROR "Run again with FIX=YES to fix these errors.")
+elseif(result EQUAL "64")
+  message(FATAL_ERROR "Spell checker printed the usage info. Bad arguments?")
+elseif(NOT result EQUAL "0")
+  message(FATAL_ERROR "Spell checker returned with ${result}")
+endif()