codec2-dev build automation

[drowe67]

Following on from #8, automagically build codec2-dev under radae.
Modify README.md
Edit *.sh CODEC2_DEV path

Skills: cmake

[tmiw]

Since codec2-dev is only used for test, any value in also suppressing its build unless unit tests are enabled?

On that note, perhaps lpcnet_demo, FARGAN etc. should also only be built if tests are enabled. Currently freedv-gui pulls its own copy of Opus for its build, so in effect Opus/FARGAN are built twice. Should that be tracked as a separate issue?

[drowe67]

This repo has served it's purpose (see Scope statement), and I don't want us to get bogged down in unnecessary maintenance. Time to move on from this repo, if you have some spare cycles, let start working on #28 (4) "C port of core ML".

I'll filter out/remove the Issues in this repo at some point.