Rename the project 'subsurface'

I never really liked 'diveclog' as a name - it's not like the C part is
all that important.  And while I could try to just make up another slang
word for despicable person (in the tradition of naming all my projects
after myself), I just can't see it.

So let's just call it "subsurface".

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>