Remove autotools generated files, eliminate hardcoded DEFBASE, add .travis.yml

- Other autotools-based projects I see in Github don't check in all the code-generated junk. They usually include an `autogen.sh`  script for running autoconf to generate that stuff. So, removed all those ugly files. Instead, interested parties should DIY by invoking `autogen.sh`
- Got rid of `DEFBASE` by using `@abs_top_builddir@` macro in `autoconf`.
- Autotools insists on `COPYING`, `README` files by default. Added `foreign` option to `AM_INIT_AUTOMAKE` which makes it not insist on those anymore, and removed those files which were duplicative of `README.md` and `LICENSE`
- Added a `.travis.yml` file for Travis-CI builds. No test coverage, but can at least automatically detect Linux build breaks when you commit from MacOS. To activate Travis CI:
  - Login to https://travis-ci.org using Github credentials
  - Click `+` icon
  - Set `sourcedelica/unix-cb` to ON
  - Travis-CI will automatically build any subsequent push to the master branch of the repo. To add a "build passing' indicator, change first 2 lines of README.md to

```
# unix-cb [![Build Status](https://travis-ci.org/sourcedelica/unix-cb.svg?branch=master)](https://travis-ci.org/sourcedelica/unix-cb)
```