Added make_archivable script for spectral pipe products to archive.
Added *.vdata files to .gitignore

These are temporary output files from the spectral pipe.  They
are used to store velocity axis information from GBTIDL for plotting
in the png files.
Made better use of tuple unpacking in loops. (no-op)
Minor variable rename for readability (no-op)
Added recompile script for spectral pipeline.

This is useful for developement so that we can recompile changes
and reuse them in an existing gbtidl session.