Add support for void sequences (2nd iteration)

[alexbestul]

Supersedes PR #454
Resolves Issue #451

[alexbestul]

This PR addresses the feedback in #454. I decided to open a new PR because the changes included renaming several files and rebasing the branch, which would have clobbered the history/comments on the existing PR.

A few things worth mentioning:

• I only added the license text to new files that I created--not to any existing files that I modified. I'm not sure of the legal implications of me adding the license to existing code :-) .
• I left all of my work-in-progress commits intact for now. Once you give a thumbs-up on the changes, I can squash them (or, of course, you can use GitHub's "Squash and Merge" option to the same effect).
• I did try adding Async again. I got it to work without affecting any existing APIs, but my implementation seemed pretty kludgy. I think it's better to get the non-async API merged, and then revisit async another day.

[stakx]

Thanks a lot for the changes, this is looking good & mergeable. There are a few minor details, mostly typos (see line comments). If you want to adjust these & do the commit squashing yourself, feel free to do so; otherwise, I'll squash-merge this in about 10 hours.

[stakx]

#451 isn't strictly wrong, as it still gives people a link to the GitHub issues and discussions, but I guess #463 would be more accurate now. :-)

[stakx]

Typo: Exuecute → Execute

[stakx]

Note that as there are other typos in Moq's code base, I'm OK with letting this stand, then do a focused typo hunt across the whole solution sometime in the future. (But of course you can fix it now if you want.)

[stakx]

Typo: Exuecute → Execute

[stakx]

Typo: Exuecute → Execute

[stakx]

I only added the license text to new files that I created--not to any existing files that I modified. I'm not sure of the legal implications of me adding the license to existing code :-) .

I think you did the right thing. After all, the purpose of your PR is adding a new feature, not fixing other pre-existing stuff. ;) Adding the license text to existing files wouldn't have hurt, I believe, but it's probably more efficient to do a separate and focused "add missing license texts" round across the whole code base.

I left all of my work-in-progress commits intact for now. Once you give a thumbs-up on the changes, I can squash them (or, of course, you can use GitHub's "Squash and Merge" option to the same effect).

See review comment above. Both is fine with me, I'll give you a few hours if you want to do this, but I'm happy to merge as is or squash-merge.

I did try adding Async again. I got it to work without affecting any existing APIs, but my implementation seemed pretty kludgy. I think it's better to get the non-async API merged, and then revisit async another day.

Agreed. You did some solid work here, let's get it merged and worry about the async bits later!