Calc Guide, Chapter 7, updated for feedback

Hello Team

I updated Chapter 7 Formulas and Functions. It is in the Feedback folder
and need approval/rejection of the change as well as English revision.

I added the following contents
* Update on "A:A" range
* Meveral screenshots
* Contents on named ranges
* Contents on named expressions
* Contents on array formulas
* Contents on speeding up calculation
* as much as I could, change OO-styles to Libo-style

I removed
* lengthy content on several ways of rounding
* misplaced example on named range

Regards