Add finders

[theofidry]

Closes #84.

[theofidry]

Not sure why Scrutinizer is failing, it might be easier to just upload the clover.xml rather than running their CI which I guess may require its own config.

I also don't have access to the Scrutinizer config but we should exclude fixtures from the inspection.

[padraic]

I've updated the Scrutinizer config.

[theofidry]

I find the Symfony Finder exclude methods not very easy to use and unhelpful. For example:

$finder = (new Finder())
    ->files()
    ->in(__DIR__)
    ->exclude(__DIR__.__DIRECTORY_SEPARATOR__.'tests')
;

with:

bin/
    foo
src/
    Foz.php
    Bar.php
tests/
    FozTest.php
composer.json

will not exclude tests/FozTest.php. So I think I'll add a blacklist-finders entry as well

[pamil]

We can leave the of callables part as it isn't asserted here.

[theofidry]

ping @padraic