Loader changes & optimizations related to issue #2551
[ci skip] Alter the welcome page
Add a changelog entry about changes in Array helper's element() and elements()
config->item() now returns NULL instead of FALSE when the required item doesn't exist.

Uniformization with other functions. This also brings the ability to properly use booleans in configuration.
Cache Driver - Backup Never Loaded
The condition that checks to see if the backup driver input is valid was prefixing the input with "cache_". Since the valid driver values don't have this prefix, the condition was always returning FALSE and the backup drivers were never being loaded.
I've removed the prefix in the condition and added a debug log message for when the backup driver is used.
Merge pull request #2555 from refringe/develop

Cache Driver - Backup Never Loaded
Fixes in JavaScript Library
Merge pull request #2556 from vlakoff/develop-4

Fixes in JavaScript Library
Update Email lib docs
Update Encrypt lib docs
Update Upload lib docs
Adjustments to the previous commit
Uniformize slash_item() with item()
Fix #2558
Fix #2560
Form helper: refactor form_open() and _attributes_to_string()
More logical order
Merge pull request #2565 from vlakoff/develop

Form helper: refactor form_open() and _attributes_to_string()
Merge pull request #2554 from vlakoff/develop-3

config->item() now returns NULL instead of FALSE when the required item doesn't exist.
Complete 3.0 upgrade notes about NULL returned on missing items