Add elimination algorithms mcs, rcm, and mmd.

[samuelsonric]

This pull request adds some additional elimination algorithms:

• mcs: maximum cardinality search
• rcm: reverse Cuthill-Mckee
• mmd: multiple minimum degree

The first two algorithms were implemented by me, and the third was taken from Sparspak.jl and lightly edited. The third algorithm, in particular, is quite good: it was the state of the practice before AMD, and it has the advantage of being MIT licensed.

[samuelsonric]

I saw the issue with ManifoldsBase on my computer as well; I don't think it's related to my additions.

[samuelsonric]

More algorithms here.

[dehann]

Hi, acknowledged thanks -- will look soon. Thanks for the contribution, more elimination algorithms are definitely good!

[samuelsonric]

Verson 0.5 has fewer dependencies. I also commented out the problematic manifolds tests.

[dehann]

Update: I haven't forgotten -- been extra busy here with passing of a family member. Looking to work through this during travel this weekend. Apologies for the delay.

[samuelsonric]

I am sorry to hear that. Please take your time!

[dehann]

Thanks for the contribution. Hangup was new ManifoldsBase v1 update happening simultaneously in related repos. Having to fix them all together. Apologies for the delay

[dehann]

will resolve these in separate PRs