Remove RACMaybe and -asMaybes
Added RACEvent class, representing any stream event
Add a name to -ignoreElements
Added -materialize
Added -dematerialize
Refactor -collect using -aggregateWithStartFactory:combine:

Also handle nils properly.
Rewrite -any: and -all: in terms of -materialize
Refactor -sequenceNext: using -materialize
Use -materialize instead of -asMaybes in GHAPIDemo
Fix typo
Merge pull request #270 from github/materialize

Replace -asMaybes with -materialize/-dematerialize