Remove duplicate description blocks

Latex no longer likes

\begin{description}
\begin{description}
\item xx
\end{description}
\end{description}

complaining that there are no items in the description. Removing the
duplicates fixes the problem. Also changed the first line to documentclass
for latex2e.
Allocate extra memory for map rebinning.

Changing multithreading scheme for smf_rebinmap1.c requires some extra
memory. Each accumulator map is now nw times longer so that each thread
can accumulate into its own map. Instead of simply pointing to output maps
on first chunk, now need to do a memcpy on the first chunk (only).
Modify smf_checkmem_map.c for new memory usage.
Update smf_rebinmap1.c for alternate rebinning scheme.

Instead of breaking up the map into nw chunks and each thread looping over
all data to find samples that fall in its chunk, instead chunk up data by
bolometer and have each thread rebin into its own temporary map. The maps
are combined into the front of the map arrays during final normalization
step (when AST__REBINEND flag is set).