Add submodules (project-chip#1262)

As we start to add other build systems, we should have a way to sync the
project without depending on make. Use git submodules for this.

This also avoids an issue with branch based subrepository management
where it's not possible to recreate historical states of the project,
which necessarily includes the state of dependencies. Tracking and
recreating prior versions is the main purpose of source control.

.gitignore

@@ -22,13 +22,6 @@ src/include/BuildConfig.h.in~
 
 # Repos stuff
 .repos-warning-stamp
-third_party/nlassert/
-third_party/nlfaultinjection/
-third_party/nlio/
-third_party/nlunit-test/
-third_party/mbedtls/
-examples/common/m5stack-tft/
-examples/common/QRCode/repo/
 
 # Example specific rules
 examples/**/sdkconfig

.gitmodules

@@ -0,0 +1,21 @@
+[submodule "third_party/nlunit-test/repo"]
+	path = third_party/nlunit-test/repo
+	url = https://github.com/nestlabs/nlunit-test.git
+[submodule "third_party/nlio/repo"]
+	path = third_party/nlio/repo
+	url = https://github.com/nestlabs/nlio.git
+[submodule "third_party/nlfaultinjection/repo"]
+	path = third_party/nlfaultinjection/repo
+	url = https://github.com/nestlabs/nlfaultinjection.git
+[submodule "third_party/nlassert/repo"]
+	path = third_party/nlassert/repo
+	url = https://github.com/nestlabs/nlassert.git
+[submodule "third_party/mbedtls/repo"]
+	path = third_party/mbedtls/repo
+	url = https://github.com/ARMmbed/mbedtls.git
+[submodule "examples/common/QRCode/repo"]
+	path = examples/common/QRCode/repo
+	url = https://github.com/nayuki/QR-Code-generator.git
+[submodule "examples/common/m5stack-tft/repo"]
+	path = examples/common/m5stack-tft/repo
+	url = https://github.com/jeremyjh/ESP32_TFT_library.git