composer.json: added "type" key & required PHP version & extension

Signed-off-by: Jan Pecha <janpecha@email.cz>
composer.json: updated description

Signed-off-by: Jan Pecha <janpecha@email.cz>
readme.md: updated

Signed-off-by: Jan Pecha <janpecha@email.cz>
PhpDepend: added description to methods

Signed-off-by: Jan Pecha <janpecha@email.cz>