Support for collections

At least 3 additional types should be supported: `Seq`, `List`, `Map` to allow users to add single entries, i.e. for
```
@builder case class Foo(ints: Seq[Int])
```
user should be able to invoke
```
.withInts(ints: Seq[Int])
```
or
```
.withInts(int: Int, ints: Int*)
```
or just append to that collection
```
.appendInt(int: Int)
```
so that `append` can be invoked multiple times.