Enrich README with explanation of AMPL code (#31)

* Enrich readme with explanation of AMPL code.
* Remove Itools comments.
* Some traduction/references.
* Add impedance handling.
* Remove french.
* Test equation.
* Refactor Input.
* add todo.
* refactor part 5 and 6.
* refactor latex.
* Modify paragraph on non-linear solver.
* Improve part on P/Q units' domain correction.
* Improve ACOPF part.
* Add reactive-diagram.PNG image.
* Apply style to reactive-diagram.PNG image.
* add left/right to improve equations.
* improve equations form.
* fix typos.
* Modify with suggestions.
* Remove some comments.

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Signed-off-by: parvy <pierre.arvy@artelys.com>