added support for inverse FFTs
now explicitly checking for $in==null
Switched to using the more basic planning functions

I was using the functions that supported variable nembed, but it looks like
PDL::PP doesn't support this anyway, so I'm not going to worry about it for now.
In some uncertain future, this will get fixed, but it's not worth the work right
now
renamed template.c
removed unneeded assertions. I check these at the perl level
implemented real FFTs. Backward doesn't work yet; no tests yet