Fix missing paren.
Fix a couple of copy-and-paste errors in Rx.Subscription documentation.
Fix a couple of proofreading errors in Rx.Notification and Rx.Observer documentation.
Merge pull request #439 from scouten/proofreading

Proofreading
Introduced withLatest() operator (src, tests, docs)
Adding worzone
Adding more worzone
Fixing fromEvent behavior for Issue #437
Updating contributing guide to RxJS
Updating contributing guide with tessel
Renamed withLatest to withLatestFrom, reverted dist
Merge pull request #441 from staltz/withlatest

Introduced withLatest() operator (src, tests, docs)
Updating dist to close Issue #441
Code cleanup
Adding pairs tests
Fixed broken link to Empty operator
Merge pull request #442 from artemyarulin/patch-1

Fixed broken link to Empty operator
Redoing documentation for mapping