Actual building + STDIO

Started work on infrastructure for unit testing. First issue: steganos binary doesn't build. A proper unit test would have found this, by the way... and I was starting to write one, noticing that the main binary was missing :whale:.

(That's a fail whale)

Also, added standard I/O handling (buffered, press Enter to actually send). This will be useful for writing an automated test, but needs proper EOF handling.