Merge either into transformers

[Yitzchak Gale]

Roman Cheplyaka wrote in February 2014:
>> I proposed to merge either into transformers more than a year ago[1],
>> and everyone seemed to agree. Could you please do it?
>>
>> [1]: http://www.haskell.org/pipermail/libraries/2012-December/019027.html

Ross Paterson responded:
> Not everyone agreed when we discussed this last August.  My proposal then
> was to introduce a new constructor ExceptT on the same pattern as ReaderT,
> etc, and to deprecate ErrorT, and that's what I intend to include in the
> next major release, after GHC 7.8 comes out.

First of all, GHC 7.8 is well past. Now we are well into the 7.10 zone.

I re-read the original thread and did not find anyone who disagreed with
this, so I'm not sure what you mean by that.

I also didn't find any mention of ExceptT there. The discussion was about
merging the either library into transformers as is, with the bits that
are problematic due to non-base dependencies written out by hand
where possible or else omitted.

That said, I think everyone will support you, without bikeshedding, if
you decide to change any of the names and/or deprecate ErrorT.

Thanks,
Yitz