Adds Sequence(start, stop, [step]); closes morelinq#240

Swap FillForward/Backward filler function args

It is more natural to supply the "current" item first.

2.0 

2.0 beta 6

2.0 beta 5

2.0 beta 4

2.0 beta 3

2.0 beta 2

2.0 beta 1

Bumping versions for release 1.4