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/configs/README.txt

@@ -0,0 +1,26 @@
+This directory contains example configuration files.
+
+The examples are generally focused on a particular usage case (eg, support for
+a restricted number of TLS ciphersuites) and aim at minimizing resource usage
+for this target. They can be used as a basis for custom configurations.
+
+These files are complete replacements for the default config.h. To use one of
+them, you can pick one of the following methods:
+
+1. Replace the default file include/mbedtls/config.h with the chosen one.
+   (Depending on your compiler, you may need to adjust the line with
+   #include "mbedtls/check_config.h" then.)
+
+2. Define MBEDTLS_CONFIG_FILE and adjust the include path accordingly.
+   For example, using make:
+
+    CFLAGS="-I$PWD/configs -DMBEDTLS_CONFIG_FILE='<foo.h>'" make
+
+   Or, using cmake:
+
+    find . -iname '*cmake*' -not -name CMakeLists.txt -exec rm -rf {} +
+    CFLAGS="-I$PWD/configs -DMBEDTLS_CONFIG_FILE='<foo.h>'" cmake .
+    make
+
+Note that the second method also works if you want to keep your custom
+configuration file outside the mbed TLS tree.