Better build system and version handling (#522).

In particular:
- version number is determined automatically, from git tags
  and it may be a released version like 0.6.5, or a version
  between two releases like 0.7.0-pre+518.badcafe. See
  bootstap.sh for the exact method of constructing it.
- do not need to build the C library or even run configure
  before building the R package. The current way of building the
  R package is
  ./bootstrap.sh
  cd interfaces/R
  make
- R package version number if slightly different, because
  the format is less flexible.
- Date of R package is filled in automatically.
- Removed some unneeded files from the 'make dist' tarball

Still TODO:
- update C test cases to pass without having to edit the
  version strings in the expected output files.
- update Python package to get the version number from the
  VERSION file.
C tests handle version strings embedded in outputs (#522).