Support for nodejs release candidates

[misterdjules]

See nodejs/node-v0.x-archive#14412 for more details on a
proposal to include release candidates in Node.js' release process.

The goal of this PR is first to get some initial feedback on:

1. Having release candidates done during Node.js' release process.
2. The actual change, and the nomenclature that has currently been chosen for these release candidates releases (the (-rc\d+)? addition to the ls-remote regexp).

This change has been tested with a "fake" release candidate of Node.js available here: https://nodejs.org/dist/v0.12.3-rc1/.

[ljharb]

Does this work with all of nvm use, nvm install, a .nvmrc file, nvm alias, nvm uninstall, nvm ls, nvm ls-remote?

It's really unfortunate that this decision was made without even checking with version managers - the existence of that release candidate is breaking nvm (see #711).

[misterdjules]

This change has been tested only with nvm install v0.12.3-rc1. The goal of this PR is to get initial feedback on:

1. The concept of having release candidates.
2. The steps that need to be taken to ensure that this doesn't break users of nvm or other versions managers.

I will do additional testing with all the commands you mentioned above, thank you! This time though I will not use nodejs.org to host the release candidates when testing.

Last but not least, this decision to have release candidates has not been made yet. The purpose of this PR is to check with version managers first, like the original comment says:

The goal of this PR is first to get some initial feedback

The reason why the v0.12.3-rc1 was still available on nodejs.org is a mistake on my side, it should not have stayed there and was used for testing purposes. It's been removed, I apologize for the confusion.

[ljharb]

Per nodejs/node#1854 (comment), I'll be adding io.js rc support, and future node versions will follow the same format.

[ljharb]

Closing this in favor of #779. Thanks for the contribution!