Support ClassName include '_'

```php
./bin/phpmig generate Class_A ./migrations
#show +f ./migrations/[]_Class_A.php

#[]_Class_A.php
class Class_A extends Migration
{
//...
}

#somecode
            $class = preg_replace('/^[0-9]+_/', '', basename($path));
            $class = str_replace('_', ' ', $class);
            $class = ucwords($class);
            $class = str_replace(' ', '', $class);

#oops  Could not find class "ClassA"
```