Move the RPN structures to a separate header file.
A work in progress

Got the sign and exponent information for compressed fields.

Now, onto the mantissa...
Factored out the Lorenzo predictor code.

Also, fixed a bug when reading a bitstream - the next valid token may not be
right after the last stream, it could be in the next 32-bit word.

Still only have sign and exponent, will work on mantissa next.
Got the mantissa.

Now just need to stitch the sign, exponent, and mantissa together.
First working version.

Still kind of slow.
Add and option to squash the forecast axis into the time axis, for rpn2nc.
Pre-load compressed records into a memory buffer.

This is much faster than incrementally fread'ing through bit streams.
Merge branch 'compressed'
Merge branch 'squash_forecasts'
Version 0.5.0