igcd, ilcm: accept list of integr
Docs updated
Intro and module structure completed.
logo: Upload the *.svg source of the logo.
logo: Implement the generation of logos of variouse formats and kinds.

Cleaning of *.svg file:

    - make the tail of the snake to be transparent.
    - remove xmlns:inscape and xmlns:sodipodi attributes.
    - insert the title and description.
    - determ, rearrange and comment the parts of of svg elements.
    - regroup the svg parts logically.
    - align SymPy text to its center.
    - set a size of logo picture to be square.
    - upper Integral on the left edge of cube

Generation of files:

    ./bin/generate_logos.py --all
logo: fix typo
logo: Update logo.txt
logo: Rename logo.txt and merge it with LogoInfo.txt.
logo: fix alignment of integral symbol and '['.
logo: reorganisation to use Makefile.
logo: Try Sigma to be scaled in Mac OS.
logo: Use Comuter Modern fonts.
logo: create version where text is path.
Create info.txt.
Fix logo-info.txt: dos -> unix fileformat
Minor formatting fixes in generate_logos.py
Remove some ambiguous short options for generate_logos.py
Fix logo target in doc/Makefile
Autogenerated files are now in doc/_build/logo/; fix logo-info.txt accordingly
Finished the tutorial