[api] Writers

[Gmugra]

Initial concept:

• (?) net.cactusthorn.config.core.Accessible should get method to provide "meta" information about property e.g. info about separators for collections.
• New Writer Interface with method: void write(net.cactusthorn.config.core.Accessible accessible)
• Sure need Writer implementatin for each file format based on URI pattern (same like with Loaders)
• New WriterFactory class with static(?) method Writer create(String uri)
• WriterFactory use SPI to load Writer implmenetations (same way like with Loaders)

Usage something like that:

@Config public interface MyConfig extends Accessible {
...
}

MyConfig myConfig = ConfigFactory.builder().addSource("file:/myconfig.properties").build().create(MyConfig.class);
Writer writer = WriterFactory.create("file:~/myconfig.toml");
writer.write(myConfig); //save data in TOML format  in user home directory.