The long road to quadrants - Documentation reorganization outside of the reference material

[andreas-kupries]

Ref: #116

This PR contains the work to restructure the documentation outside of the reference material for higher clarity, especially to prospective new users.

To review check out the PR's branch, and then open the file embedded/www/files/critcl_introduction.html in a browser.

Deep material irrelevant to users, especially new users is gone, the quadrants are noted, and filled.

The documents in the howto quadrant are all rewritten to be more active, old material removed, more things pushed out of scope to other sites. They form a sequence from getting sources to using critcl, with the last incomplete and currently worked on.

[andreas-kupries]

The old entry point embedded/www/files/critcl_introduction.html is now embedded/www/files/critcl.html. Alternatively it should now also be the first link in the embedded/www/toc.html, i.e. the table contents.

[andreas-kupries]

Accumulated work pushed. Please review.