Add optional openssl support

The PR includes a commented out option in "build-all.sh" for including OpenSSL binaries.

It clones this repo and builds "openssl.a" and "libcrypto.a" binaries : https://github.com/Zen-CODE/ios-openssl

There are still some optimizations that can be done in terms of which architectures we need to build for (see lines 85 to 89 of: https://github.com/Zen-CODE/ios-openssl/blob/master/build.sh), but it works (on my machine at least, from a clean checkout). These optimizations can come in time.

Suggestions/feedback welcome :-)