Print to stderr

[jhtu]

There are a few warnings in vectorspace.py related to how many vectors can be loaded, etc. I think it makes sense for these to be printed to stderr, not stdout, as that is where warnings and errors typically go. There is also an estimate for the amount of time that all the inner products will take. I think it might make sense for this to print to stderr as well, as it is sort of an auxiliary/unnecessary message.