Freeze libraries needed by adafruit_circuitplayground library into firmware.

This saves a lot of RAM. Fixes #287.
Also fixed compilation of frozen_mpy.c to use supplied make rule rather than
builtin rule (supplied rule suppresses printing out the gcc command line).

.gitmodules

@@ -20,3 +20,12 @@
 [submodule "atmel-samd/frozen/Adafruit_CircuitPython_NeoPixel"]
 	path = frozen/Adafruit_CircuitPython_NeoPixel
 	url = https://github.com/adafruit/Adafruit_CircuitPython_NeoPixel
+[submodule "frozen/Adafruit_CircuitPython_Thermistor"]
+	path = frozen/Adafruit_CircuitPython_Thermistor
+	url = https://github.com/adafruit/Adafruit_CircuitPython_Thermistor.git
+[submodule "frozen/Adafruit_CircuitPython_LIS3DH"]
+	path = frozen/Adafruit_CircuitPython_LIS3DH
+	url = https://github.com/adafruit/Adafruit_CircuitPython_LIS3DH.git
+[submodule "frozen/Adafruit_CircuitPython_BusDevice"]
+	path = frozen/Adafruit_CircuitPython_BusDevice
+	url = https://github.com/adafruit/Adafruit_CircuitPython_BusDevice.git

atmel-samd/boards/circuitplayground_express/mpconfigboard.mk

@@ -7,4 +7,7 @@ FLASH_IMPL = spi_flash.c
 CHIP_VARIANT = SAMD21G18A
 
 # Include these Python libraries in firmware.
+FROZEN_MPY_DIRS += $(TOP)/frozen/Adafruit_CircuitPython_BusDevice
+FROZEN_MPY_DIRS += $(TOP)/frozen/Adafruit_CircuitPython_LIS3DH
 FROZEN_MPY_DIRS += $(TOP)/frozen/Adafruit_CircuitPython_NeoPixel
+FROZEN_MPY_DIRS += $(TOP)/frozen/Adafruit_CircuitPython_Thermistor

frozen/Adafruit_CircuitPython_BusDevice

@@ -0,0 +1 @@
+Subproject commit 39f28ed4e0e5a06fc33fd01c1efc8c52c4140f03

frozen/Adafruit_CircuitPython_LIS3DH

@@ -0,0 +1 @@
+Subproject commit fa00b61d1bde90c3cf9cce74388cb9717058b2be

frozen/Adafruit_CircuitPython_Thermistor

@@ -0,0 +1 @@
+Subproject commit 2d57c0ba9a09d6d30f0ae2b98aba9567c25e6fb6

py/mkrules.mk

@@ -46,6 +46,12 @@ vpath %.c . $(TOP)
 $(BUILD)/%.o: %.c
 	$(call compile_c)
 
+# frozen.c and frozen_mpy.c are created in $(BUILD), so use our rule
+# for those as well.
+vpath %.c . $(BUILD)
+$(BUILD)/%.o: %.c
+	$(call compile_c)
+
 # List all native flags since the current build system doesn't have
 # the MicroPython configuration available. However, these flags are
 # needed to extract all qstrings