Added coupon loop documentation
Merge pull request #68 from roadster31/in_use

Added coupon loop documentation
Update product_sale_elements.md

Added $IS_DEFAULT, $REF
Merge pull request #67 from bibich/improvements

- small fixes on loop
- added missing substiutions
loop doc
   - getArgDefinitions instead of defineArgs
   - bad link on localhost
   - loop name must be lowercase
   - missing 'use'
   - buildModelCriteria must return a query, not a collection
Merge pull request #71 from griotteau/patch-loop

error in loop documentation
fixed auth loop
Added output parameter PSE_COUNT for product loop
Fixed typo