Optionally disable PMRRR

[rhl-]

In an effort to close #21 I tried to create an appveyor build. One failure that occured was in PMRRR builds. Since we how have an alternative Elemental-only implementation of the D&C EVD it seems we do not need PMRRR as a hard dependency any longer. There may be some performance penalty on Windows, but its a small price to pay for having a build.

This was not the only blocker however.