Some changes to functions which create documents.
Some changes to functions which create documents.

- imports are moved to top-level
- doc string is added to createDocumentForPrefix function
- doc string is added to createDocument for GSoC
- doc string is added to createDocument for GCI
- order of parameters is changed

It addresses comments for revision 49af40c8e6f6.

rhyolight/nupic.son,rhyolight/nupic.son,rhyolight/nupic.son