pkg: add support for tinycrypt

pkg/tinycrypt/Makefile

+PKG_NAME=tinycrypt
+PKG_URL=https://github.com/01org/tinycrypt
+PKG_VERSION=3ea1a609e7aff9f2d8d13803e1076b7a8e551804
+PKG_LICENSE=BSD-3-Clause
+
+.PHONY: all
+
+all: git-download
+	"$(MAKE)" -C $(PKG_BUILDDIR)/lib/source/ \
+			  -f $(RIOTPKG)/tinycrypt/Makefile.$(PKG_NAME)
+
+include $(RIOTBASE)/pkg/pkg.mk

pkg/tinycrypt/Makefile.include

+INCLUDES += -I$(PKGDIRBASE)/tinycrypt/lib/include

pkg/tinycrypt/Makefile.tinycrypt

+MODULE = tinycrypt
+
+include $(RIOTBASE)/Makefile.base

pkg/tinycrypt/doc.txt

+/**
+ * @defgroup pkg_tinycrypt tinycrypt crypto library
+ * @ingroup  pkg
+ * @brief    Memory optimized crypto library for embedded devices
+ * @see      https://github.com/01org/tinycrypt
+ */