Structural changes/description:

Use dynamic checks for filesystem functions, headers, and
structure fields via configure. This allows us to get away from
the __FreeBSD_version complexity I embedded in pjdfstest some
years ago (which is both hard to maintain and can be incorrect if
someone backports a filesystem feature and doesn't change
__FreeBSD_version, appropriately). Plus it moves way from the
hardcoded (incorrect) feature list for Linux and OSX, and as a
bonus will enable posix_fallocate testing.

Build process changes:

- Replace Makefile with Makefile.am (the automake Makefile snippet).
-- autoconf/automake is now required to build the project (see the
   README file for more details).
-- Add `-Wall -Werror` to AM_CFLAGS to catch silly coding errors (it
   was `-Wall` previously).
- Adjust the build steps in travis/build.sh to call the steps
  documented in the README file.

Documentation updates:
- Update the build/test directions in README.
- Add AUTHORS file, noting who authored the code and maintains it.
- Rename LICENSE to COPYING to quiesce complaints from automake.

Miscellaneous changes:
- Add empty files to placate automake: ChangeLog, NEWS.
- Add autoconf/automake/configure generated files to .gitignore .

Fix notes:
* The posix_fallocate bonus enhancement fixes #14.
* The overall autoconf work fixes #21.