Markdownify `README.md` and remove obsolete `.bat`s

The old dead links in readme.txt have been updated/removed, and some
typos fixed. README.md has been added to source tarball via
`extra-source-files`.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
Attempt to integrate test-suite w/ Cabal and Travis-CI

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>