Added wolfSSL Compatability for Asio

[MJSPollard]

This PR enables the user to compile a program using Asio with the current version of wolfSSL instead of OpenSSL.

To build wolfSSL and configure wolfSSL for Asio use, clone the wolfSSL repo from Github and execute the following commands from the root directory.

$ ./autogen.sh
$ ./configure --enable-asio
$ make
$ sudo make install

After, to build Asio with wolfSSL to make use of the Asio unit tests, run the following commands from the asio/asio/ directory.

$ ./autogen.sh
$ ./configure --with-wolfssl=/usr/local  (change path according to where wolfSSL was installed)
$ make
$ make check

To build an application using wolfSSL with Asio, do it the same, except add #include<wolfssl/options.h> to the top of an application file that uses SSL or TLS. An example command to compile the application correctly is as follows.
g++ app.cpp -I/usr/local/include/wolfssl -lwolfssl -lpthread

For more questions or to learn more about wolfSSL please visit our website.

[chriskohlhoff]

Addressed in asio version 1.14.1.

[tomoveu]

@chriskohlhoff could you please get attention to this?

This original PR was not cherry picked correctly and this resulted in issue #574

I assume there was a good reason not be directly merged, but the cherry pick missed a file.