Upload homebrew artifact for the c++ binding to releases. about ironoxide-swig-bindings

[coltfred]

I started this work over on the osx_build branch. I renamed the library to ironoxide.

We need to change crate-type to staticlib on the machine that's doing the ironoxide ios build (which must be on OSX).

After setting up the crate-type, we should install cargo-lipo. Then we should run cargo lipo --release in the cpp dir. Once we do that, we should upload it to the release as ironoxide_ios.a.

We want to do the ios suffix in the release so if we produce a different lib later which is statically linked we can handle it.

[coltfred]

Instead of just uploading the .a file for ios, we'll instead want to make a single tar which will be the thing that our homebrew recipe will download.

The form of the tar should be this:

├── headers
├── ironoxide.pc.in
└── libironoxide.a

headers is a dir with all the headers (the files from cpp/generated/sdk)
ironoxide.pc.in is a file with the following in it:

prefix=%PREFIX%
exec_prefix=${prefix}
includedir=${prefix}/include
libdir=${exec_prefix}/lib

Name: ironoxide
Description: The ironoxide library
Version: 0.13.1
Cflags: -I${includedir}/ironoxide
Libs: -L${libdir} -lironoxide

We should tar this up and call it ironoxide-homebrew.tar.gz.