Modification of "as-is" to be empty valued (Instead of boolean)

[stephenbanghart]

As per changes in the Profile Resolution Specification (#1017), "as-is" (profile:merge:combine:as-is) needs to be changed to an empty value field instead of a boolean.

Since only one of the optional children (flat,as-is,custom) may appear in a given "merge", the field's existence is sufficient to indicate the mode.

[david-waltermire]

We can't do this in 1.x, since it will be a backwards compatible breaking change. I'll add this to 2.0. We can deprecate the merge structure and replace it with a new/better structure in the near term. This should be made a new issue.