Feature/mbedtls (#84)

* try to import mbedtls and build it

* add stubs socket class

* some boilterplate, read and write function implemented

* more boilterplate / current error in handshake because no CA cert is setup

* add something so skip ca verification, can ws curl https://google.com !

* cleanup / close implemented

* tweak CMakefiles

* typo in include

* update readme

* disable unittests

third_party/mbedtls/crypto/programs/psa/key_ladder_demo.sh

@@ -0,0 +1,49 @@
+#!/bin/sh
+set -e -u
+
+program="${0%/*}"/key_ladder_demo
+files_to_clean=
+
+run () {
+    echo
+    echo "# $1"
+    shift
+    echo "+ $*"
+    "$@"
+}
+
+if [ -e master.key ]; then
+    echo "# Reusing the existing master.key file."
+else
+    files_to_clean="$files_to_clean master.key"
+    run "Generate a master key." \
+        "$program" generate master=master.key
+fi
+
+files_to_clean="$files_to_clean input.txt hello_world.wrap"
+echo "Here is some input. See it wrapped." >input.txt
+run "Derive a key and wrap some data with it." \
+    "$program" wrap master=master.key label=hello label=world \
+               input=input.txt output=hello_world.wrap
+
+files_to_clean="$files_to_clean hello_world.txt"
+run "Derive the same key again and unwrap the data." \
+    "$program" unwrap master=master.key label=hello label=world \
+               input=hello_world.wrap output=hello_world.txt
+run "Compare the unwrapped data with the original input." \
+    cmp input.txt hello_world.txt
+
+files_to_clean="$files_to_clean hellow_orld.txt"
+! run "Derive a different key and attempt to unwrap the data. This must fail." \
+  "$program" unwrap master=master.key input=hello_world.wrap output=hellow_orld.txt label=hellow label=orld
+
+files_to_clean="$files_to_clean hello.key"
+run "Save the first step of the key ladder, then load it as a master key and construct the rest of the ladder." \
+    "$program" save master=master.key label=hello \
+               input=hello_world.wrap output=hello.key
+run "Check that we get the same key by unwrapping data made by the other key." \
+    "$program" unwrap master=hello.key label=world \
+               input=hello_world.wrap output=hello_world.txt
+
+# Cleanup
+rm -f $files_to_clean