Rename taint to halt, and clean/dirty to ongoing/halted

[waiting-for-dev]

This makes the purpose clearer and avoids overriding Object#taint

Now, instead of Conn::Clean and Conn::Dirty subclasses we have Conn::Ongoing and Conn::Halted. Also, in order to stop the pipe we need to call #halt instead of #taint. A #halted? predicate has been added to Conn.

[timriley]

I really like these naming changes, @waiting-for-dev :) "Taint", "unclean", etc. raised a lot of negative connotations for me. Ongong/Halted etc. seem both more descriptive and more neutral. Kudos 👏

[waiting-for-dev]

Thanks @timriley :) Yep, those names were more related to the design principles in the implementation that to the real purpose in this concrete library...