Refactor Wiki pages

[SergeStinckwich]

Some pages of the Wiki are obsolete. Someone need to have a look and refactor&clean the code a little bit: https://github.com/PolyMathOrg/PolyMath/wiki

[macie]

Hi,
some wiki pages links to pages from non-existent SergeStinckwich/SciSmalltalk repo. For example links at https://github.com/PolyMathOrg/PolyMath/wiki/SciSmalltalk-Contents#math-ode

Maybe wiki pages could be edited by everyone? Or - better - content from wiki could be moved to markdown files inside new /docs directory (at root level of repo). Then everyone will be able to safely edit wiki (by pull requests).