updated documentation for "attrValueProcessors" and "valueProcessors"

[claasahl]

Updated documentation of callbacks for "attrValueProcessors" and "valueProcessors" in section "Options" of README.md.

Before:

function (name){
  //do something with `name`
  return name
}

After:

function (value, name) {
  //`name` will be the node name or attribute name
  //do something with `value`, (optionally) dependent on the node/attr name
  return value
}

[coveralls]

Coverage remained the same at 97.633% when pulling 3637fa1 on claasahl:master into d057cd9 on Leonidas-from-XIV:master.

[jcsahnwaldt]

Correct. The signature in the Options section was wrong. This patch copies the signature from the Processing attribute, tag names and values section, which is correct.

[jcsahnwaldt]

This PR would have been a nice improvement, but it was closed without being merged. :-( I don't know why it wasn't merged...

[jcsahnwaldt]

There's a similar (but less complete) PR now: #474

[Leonidas-from-XIV]

Well, let's go with #474 now, the code here is gone.