Improve definition of filterables fields

[lorado]

Hi. Here is me again... 🤣

in my project I wanted to define filterable fields type, but there was no option to do it. So I improved parsing of given values:

• There is new TypedFilterInterface, with method getType(), that should return wished input type. This type will be used, if instance of class that implements TypedFilterInterface defined in YourDefinition::getFilterables()
• there is still ability to define input type via array. So with array devinition it is possible to define type and use a closure (see examples below)
• all possible definitions are tested with unit tests

So here are all possible definitions of filterables:

// NOTE: ComplexFilter implements TypedFilterInterface! 
public function getFilterable() {
	return [
		// Simple equality check (or "in" if value is an array). Type is Type::json()
		'id'       => new EqualsOrContainsFilter(),
		
		// Customized filter. Type is Type::json()
		"nameLike" => function($builder, $value) {
			return $builder->whereRaw('name like ?', $value);
		},
		
		// type is Type::string()
		"anotherFilter" => [
			"type" => Type::string(),
			"resolver" => function($builder, $value) {
				return $builder->whereRaw('anotherFilter like ?', $value);				
			}
		],
		
		// type is what is returned from `ComplexFilter::getType()`.
		// This is the preffered way to define filters, as it keeps definitions code clean
		"complexFilter" => new ComplexFilter(),
		
		// type in array will be overriden by what is returned from `ComplexFilter::getType()`.
		// this kind of difinition is not clear, but is implemented for backward compatibilities. Please don't use it
		"complexFilter2" => [
			"type" => Type::int(),
			"resolver" => new ComplexFilter()
		],
	];
}

I also updated README and listed there all possible usages (as above).

There is NO breaking changes. Old definitions are still working, with default Type::json() type.

As this is already 4th pull request, after merging some of PRs may require manually merge from me. So... let me know...

[drasill]

Thank you !