User Guide update - Database Forge

Made section levels consistent with the other database reference docs.
Added return value writeups.
Signed-off-by:James L Parry <jim_parry@bcit.ca>
Fix #3380
Fix a regression from the previous commit
Improve on the fix for #3380
Regressions ... #3380 #3194 ab9217e316a79bc8fab2840c8f5bd2b9bc7a4dc0
Allow pulling multiple get/post ...etc at once
Added changelog entry
updated documentation
Fixed code style.
Merge pull request #3381 from aanbar/multiple_args_get_post

Allow pulling multiple get/post ...etc at once
Some optimizations & polishing following PR #3381
Fix an error from the previous commit
Fix the user guide writeup for the DB forge
Signed-off-by:James L Parry <jim_parry@bcit.ca>
Merge pull request #3375 from jim-parry/userguide/dbforge

User Guide update - Database Forge
Merge branch 'develop' of github.com:bcit-ci/CodeIgniter into userguide/database_utilities