Update plugins.rst

The psr-4 autoload paths should be relative, not absolute.
[fr] follow #1476

Add info about $confirmMessage arg removal.
[fr] follow #1478

Update the 'idField' and 'valueField' options
[fr] follow faf034b

Fixing syntax errors in examples
Merge pull request #1508 from oldskool/patch-4

Update plugins.rst