Added tests for wrapping preProcessors
utils/stream.js: When creating a from stream, waiting to emit data until the next tick to allow streams to be piped together first.
processorStream: Removed the built in file data cache.
directiveStream: Only apply preProcessors on self & binary streams. Before the preProcessors were run after every created stream, causing the recursion to apply several idendical preProcessors to each file.
Merge remote-tracking branch 'origin/v2.0.0' into remove-pre-processor-cache
Merge pull request #80 from jpettersson/remove-pre-processor-cache

Remove preProcessor cache