minor reorganization of the Maxima manual on-line

Hello,

I have moved the English-language html and pdf documents from 

  http://maxima.sf.net/docs/original/

to

  http://maxima.sf.net/docs/manual/en/

Likewise I've moved the Spanish and Portuguese documents from

  http://maxima.sf.net/docs/original/{es,pt}/

to 

  http://maxima.sf.net/docs/manual/{es,pt}/

In place of the main documents (maxima.html and maxima_toc.html
and their counterparts in es and pt) I've put redirect pages.

I've updated the links in http://maxima.sf.net/docs.shtml .

I'll attempt to find other links to the manual documents and update
them if I can.

I believe this reorganization is an improvement.
You'll let me know if you feel otherwise.

all the best,
Robert Dodier