added fe subproject

And also moving modules -> external to obey common dir layout
guidelines.

.gitmodules

@@ -1,18 +1,21 @@
 [submodule "abseil-cpp"]
-	path = modules/abseil-cpp
+	path = external/abseil-cpp
 	url = ../../abseil/abseil-cpp
 [submodule "doxygen-awesome-css"]
-	path = modules/doxygen-awesome-css
+	path = external/doxygen-awesome-css
 	url = ../../jothepro/doxygen-awesome-css.git
 [submodule "googletest"]
-	path = modules/googletest
+	path = external/googletest
 	url = ../../google/googletest.git
 [submodule "half"]
-	path = modules/half
+	path = external/half
 	url = ../../AnyDSL/half.git
 [submodule "lyra"]
-	path = modules/lyra
+	path = external/lyra
 	url = ../../bfgroup/lyra.git
 [submodule "modules/rang"]
-	path = modules/rang
+	path = external/rang
 	url = ../../agauniyal/rang.git
+[submodule "modules/fe"]
+	path = external/fe
+	url = [email protected]:leissa/fe.git

CMakeLists.txt

@@ -50,20 +50,22 @@ include(CTest)
 if(BUILD_TESTING AND THORIN_BUILD_TESTING)
     include(GoogleTest)
     set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
-    add_subdirectory(modules/googletest EXCLUDE_FROM_ALL)
+    add_subdirectory(external/googletest EXCLUDE_FROM_ALL)
 endif()
 
 set(ABSL_PROPAGATE_CXX_STD ON)
 set(ABSL_USE_EXTERNAL_GOOGLETEST ON)
 set(ABSL_ENABLE_INSTALL ON)
 if(NOT THORIN_INSTALL_DEPENDENCIES)
-    add_subdirectory(modules/abseil-cpp EXCLUDE_FROM_ALL)
-    add_subdirectory(modules/rang       EXCLUDE_FROM_ALL)
-    add_subdirectory(modules/lyra       EXCLUDE_FROM_ALL)
+    add_subdirectory(external/abseil-cpp EXCLUDE_FROM_ALL)
+    add_subdirectory(external/rang       EXCLUDE_FROM_ALL)
+    add_subdirectory(external/lyra       EXCLUDE_FROM_ALL)
+    add_subdirectory(external/fe         EXCLUDE_FROM_ALL)
 else()
-    add_subdirectory(modules/abseil-cpp)
-    add_subdirectory(modules/rang)
-    add_subdirectory(modules/lyra)
+    add_subdirectory(external/abseil-cpp)
+    add_subdirectory(external/rang)
+    add_subdirectory(external/lyra)
+    add_subdirectory(external/fe)
 endif()
 add_subdirectory(thorin)
 add_subdirectory(cli)