CONVERT: Add new subroutine to handle HISTORY continuation lines.

FITSIO changed so that instead of truncating long history text,
it now wraps to a new line.  Keep reading the text until a new
heading is reached.
CONVERT: Fix a number of issues to preserve history information.

This and 32f0666f8ed08 relate to Issue 32.

  -  Call the new COF_MHISR to deal with new continuation lines,
     say for long-pathed software or dataset names.
  -  Enlarge x5 paragraph buffer to cope with MAKEMAKE's explosion in
     configuration parameters.  It would be good to set this
     dynamically.

There is still an issue disriminating additional records from
continuation lines without headings.  This probably requires a change
to NDF2FITS to demarcate the records from the other components of
HISTORY structure.