curried Either and added Left and Right

properties are prepended with _ to allow functions left() and right()
isRight() added to pass strict mode

In one very real sense, all of Ramda has been an attempt to work out ideas in a practical way.  Although we work them out in a manner that we would want to use -- hence a library -- it is also a learning experience.  "Can we auto-curry everything?"  "Does function-first, data-last work everwhere?"  "Do these algebraic types make sense to normal folks like us?"  And of course there were others which we answered with a resounding "No", such as "Can we get performant recursion?"

That the results of this learning experience is helpful to others is fantastic, but was never the central goal (or at least mine.)  That is part of what has made this transition to library maintainers more difficult than it would be for someone who set out to create such a beast.