Build from submodule by default (make, cmake)

Adapt tests in all.sh:
- tests with submodule enabled (default) no longer need to enable it
  explicitly, and no longer need runtime tests, as those are now handled by
all other test cases in this script
- tests with submodule disabled (old default) now need to disable it
  explicitly, and execute some runtime tests, as those are no longer tested
anywhere else in this script

Adapt documentation in Readme: remove the section "building with submodule"
and replace it with a new section before the other building sections.
Purposefully don't document how to build not from the submodule, as that
option is going away soon.

library/Makefile

@@ -1,6 +1,9 @@
 
 # Also see "include/mbedtls/config.h"
 
+# build crypto form submodule unless explicitly disabled
+USE_CRYPTO_SUBMODULE ?= 1
+
 CFLAGS	?= -O2
 WARNING_CFLAGS ?=  -Wall -W -Wdeclaration-after-statement
 LDFLAGS ?=
@@ -64,7 +67,7 @@ endif
 endif
 
 
-ifdef USE_CRYPTO_SUBMODULE
+ifneq ($(USE_CRYPTO_SUBMODULE), 0)
 # Look in crypto for libmbedcrypto.
 LOCAL_LDFLAGS += -L../crypto/library
 LOCAL_CFLAGS += -I../crypto/include
@@ -174,7 +177,7 @@ libmbedx509.dll: $(OBJS_X509) libmbedcrypto.dll
 	$(CC) -shared -Wl,-soname,$@ -Wl,--out-implib,$@.a -o $@ $(OBJS_X509) -lws2_32 -lwinmm -lgdi32 -L. -lmbedcrypto -static-libgcc $(LOCAL_LDFLAGS) $(LDFLAGS)
 
 # crypto
-ifdef USE_CRYPTO_SUBMODULE
+ifneq ($(USE_CRYPTO_SUBMODULE), 0)
 libmbedcrypto.%:
 	$(MAKE) CRYPTO_INCLUDES:="-I../../include -I../include" -C ../crypto/library $@
 else