Add support for yanking into a register

[mathstuf]

Yanking code should support placement into a register. I've rebased this on top of recent master and haven't tested the new integration much (working on that here).

[alerque]

Fork notice: With the upstream project sitting stale after nearly 8 months since the last activity, 71 outstanding pull requests, no comments from the original developer, and dozens of developers duplicating efforts while scratching their own itches, I've decided to step in and run a fork for a while. Hopefully the original developer will eventually consider picking this plugin up again or adding more maintainers so that the user base doesn't end up fragmented, but for now I would invite anyone interested in the latest updates to consider installing from and contributing pull requests to my fork.

About this PR: I initially merged this PR as is, but later found my testing was flawed and had to revert it (see 083128c). I suspect the issue is minor, but it does stop normal function of the plugin. I could love to see this updated so it actually works when applied to my fork. Please consider rebasing and touching it up based on alerque/nerdcommenter, submit a PR to me directly, and then run the plugin from there for (so far) over two dozen other updates.

[mathstuf]

For reference, reverted in 301c733. This is a fairly invasive change, so I'm not surprised it broke when combined with lots of other changes. I'll have to see if I get the time to update this.

[mathstuf]

Sorry, commit 083128c.

[alerque]

Change of plans. Thanks to scrooloose who has added me as a maintainer to this repo, I'll be going through and taking care of business here instead of in a fork. One of the reasons I didn't just merge my fork was the way I messed up checking this PR.

I'm leaving this open, but as noted it does need some more work before being considered again. Keep us posted on how it shapes up if you get time to work with it against the master branch.

[mathstuf]

So I tested it a bit here again, seems to work on top of master.

[alerque]

I can confirm that this is working now—or at least not breaking the whole plugin like my previous merge attempt. Thanks for rebasing.

I'm a little confused about how it works though. In my testing it seems to do a line-wise yank even when the comment the cursor is in is not the full line or when it's in the middle of a multi-line block. This doesn't seem right to me. Can you add documentation to doc/NERD_commenter.txt about how this is supposed to work? That should both clarify what it is I'm testing over here and provide future users some direction on how to use the plugin.