Rename to `diaktoros` or clarify in `README.md`

[Ocramius]

As per this amazingly informative graphic representation: http://www.googlefight.com/index.php?word1=diactoros&word2=diaktoros

(and as per discussion on IRC)

Yes, it may be a typo like "symfony" (intentional), still not sure tho.

That said, this is nitpicking :-)

[bakura10]

Seems to be Diactoros ^^.

[Ocramius]

@bakura10 works for me as long as it's not considered a typo :-)

[weierophinney]

From what I've found, they're both valid spellings. The version with a "k" is the traditional Greek, while the version with a "c" is the latinized variant. Since the goal was to have something unique in the PHP namespace that had a "message" or "messenger" semantic, I think we're in good shape.