fix documentation typos

Signed-off-by: enyst <engel.nyst@gmail.com>
Add function documentation to oscad model.

Signed-off-by: enyst <engel.nyst@gmail.com>
Add documentation for oscad basics functions.

Signed-off-by: enyst <engel.nyst@gmail.com>
2013-08-21: external help integrated, better menu structure
2013-08-21: better structure, disclaimer improvements, external help integrated