See #123.

Vcsn TafKit no longer exists, it is now called Vcsn Tools.

* TODO.txt, bin/vcsn.in, build-aux/bin/coverage,
* doc/README.txt, doc/notebooks/Executables.ipynb,
* doc/notebooks/Hacking.ipynb, doc/notebooks/local.mk,
* internship.txt, libexec/local.mk, tests/bin/bench,
* tests/bin/checker, tests/bin/ipynbdoctest.py,
* tests/demo/local.mk, tests/local.mk,
* tests/python/expand.py, tests/python/local.mk,
* tests/python/reduce.py, tests/rat/common.rat,
* tests/rat/local.mk, vcsn/algos/standard.hh,
* vcsn/dyn/types.hh:
(tafkit): Rename as...
(tools): this.

* tests/tafkit/eval.chk: Rename as...
* tests/tools/eval.chk: this.
* tests/tafkit/help.chk: Rename as...
* tests/tools/help.chk: this.
* libexec/vcsn-tafkit.cc: Rename as...
* libexec/vcsn-tools.cc: this.
* libexec/vcsn-tafkit.hh: Rename as...
* libexec/vcsn-tools.hh: this.
* tests/tafkit/local.mk: Rename as...
* tests/tools/local.mk: this.
* build-aux/bin/tafkit-gen: Rename as...
* build-aux/bin/tools-gen: this.