Enhancement: Enable and configure phpdoc_line_span fixer

[localheinz]

This PR

• enables and configures the phpdoc_line_span fixer

Follows #213.

💁‍♂ For reference, see https://github.com/FriendsOfPHP/PHP-CS-Fixer/tree/v2.16.0#usage:

phpdoc_line_span

Changes doc blocks from single to multi line, or reversed. Works for class constants, properties and methods only.

Configuration options:

• const ('multi', 'single'): whether const blocks should be single or multi line; defaults to 'multi'
• method ('multi', 'single'): whether method doc blocks should be single or multi line; defaults to 'multi'
• property ('multi', 'single'): whether property doc blocks should be single or multi line; defaults to 'multi'