Improve version metadata

* flo_check_homework/__init__.py: new VersionInfo class providing
something similar to what is returned by sys.version_info.

* flo_check_homework/__init__.py: new module-level variables
'version_info' and '__version__'. flo_check_homework.version_info is a
VersionInfo instance and flo_check_homework.__version__ a string
representation of this object, giving the expected version "number" (a
string such as "0.9.11b1").

* flo_check_homework/main.py: use the new __version__ attribute.

* setup.py: use the new __version__ attribute and change the download
url to reflect the new directory layout for release tarballs (one
directory per version, with eventual sub-releases such as 0.9.11b1 being
grouped with the corresponding release [0.9.11]).
Fortify the magic word

* flo_check_homework/main.py (MainWindow.magicFormula): in order to make
"replay attacks" against the magic formula harder, implement the
following measures:
  - the magic word is now a function of 3 variables instead of 2 (use
    the source, Luke!);
  - after 3 failed attempts, the magic wand stops working;
  - ditto after the first successful attempt, since it is not needed
    anymore.
Formatting fixes
Improve game "decoration"

* flo-check-homework-decorate-games: read the input in a new XML-based
format instead of the old format with TAB separators.

* flo-check-homework-decorate-games: use argparse for options
processing.

* flo-check-homework-decorate-games: make the locales used in launcher
scripts for running flo-check-homework and for starting the games
configurable through options --fch-locale and --prog-locale, which
respectively default to fr_FR.UTF-8 and en_US.UTF-8.

* flo-check-homework-decorate-games: new options --real-dir and
--wrapper-dir, which respectively default to /usr/games and
/usr/local/games.

* fch-convert-old-data-file-to-xml: new script to ease transition from
the old "datafile" format with TAB separators to the new XML-based
format.
Introduce end-of-line normalization for text files in the repository
Release 0.9.12

* flo_check_homework/__init__.py: update the version number.

* README.rst: fix typos and update the version number.

* README.i18n: mention the requirement of a recent or patched pylupdate4
for generating or updating the .ts files.

* setup.py: minor improvement.

* flo-check-homework.fr.ts: update translation.

* Update copyright years in the recently-modified Python files.