Implement startWith() operator

[tetsuharuohzeki]

Fix #84

[benlesh]

Thanks! I'll check this out after a while unless someone else gets to it. I'm on vacation this week.

[trxcllnt]

@saneyuki thanks for the PR! Would you mind updating this file to pull in the module for the operator you're relying on here, like concat does? Since we're aiming for complete modularity, we can't assume concat will exist on the ScalarObservable prototype. I'd be satisfied with this PR if you pulled in either of the concat or merge modules, it's your choice. Thanks!

[trxcllnt]

It'd also be great if you changed this to use the ScalarObservable constructor, instead of just, since ScalarObservable isn't guaranteed to have just statically defined either.

[tetsuharuohzeki]

@trxcllnt thank you for your review!. I pushed the fixup commit.

[trxcllnt]

@saneyuki thanks! lgtm.

[benlesh]

There's no way you could know this, because we don't have contribution guidelines, but I'd really like it if you could flatten your commits and change the commit message to: `feat(operator): implement startWith"

The easiest way to do this would be an interactive rebase. git rebase -i HEAD~2 then you'd fixup the second entry, and reword the first. If you need any additional help, let me know and I'm happy to assist.

Otherwise, LGTM... let me know when you've got those changes pushed and I'll merge it in.

Thanks again!

[tetsuharuohzeki]

@Blesh

okay! I squashed my changesets & change the message to feat(operator): implement startWith().

[benlesh]

PR merged with commit 1f36d99