Minor changes to quickstart.rst
Minor changes (fix formatting / typos) in coding guidelines.
Extend C++ and Python coding rules.

- Add more information
- State that GammaLib uses C++98, not C++11
- Change statement on supported Python versions
  (was 2.4 upwards, now 2.6 upwards)
Change MAC to UNIX newline character in RST files.

For some reason most of the RST files use MAC `^M` instead
of UNIX `\n` newline characters.

This is problematic because e.g. git diff doesn't work with
MAC newlines by default and considers such files as one line,
giving meaningless results:
https://cta-redmine.irap.omp.eu/issues/558#note-10

I ran the mac2unix tool to convert MAC to UNIX newlines
as suggested here:
http://stackoverflow.com/questions/64749/m-character-at-end-of-lines
http://stackoverflow.com/questions/1889559/git-diff-to-ignore-m

Besides these RST files the GammaLib repo seems to be clean,
i.e. no other files changed when I ran mac2unix on them.
Merge branch 'dos_newline_to_unix' into integration