Adding function handlers to scs2pdf

I'm starting the process of making scs2pdf use function handlers for
different events and data.  I've made a function pointer for the functions
in scs.c and then initialized those pointers in scs2pdf.c.  I need to do
the same for the pdf_*() functions in scs2pdf.c.  Then make an intialize
function that can be called to set all the pointers to their defaults.
Once this is done lp5250d should be able to set these function pointers
according to the type of output desired and not need to run scs2* to do
the scs conversion.

Before I get too much further I would like someone to take a look at it.
It is *very* preliminary, no structures or nice stuff.  I just want to
make sure I'm headed down the right path.  Scott, you've talked to me
about this, would you mind taking a quick peek?

Once complete this should solve the win32 porting troubles.  lp5250d can
start its own event loop and set up the function pointers and poof! output
in the desired format.  Hey, my changes don't even break anything yet!

See the full source files and diff at:

http://www.eaerich.com/scs2pdf.c
http://www.eaerich.com/scs.c
http://www.eaerich.com/scs.h
http://www.eaerich.com/tn5250.diff

James Rich
james@eaerich.com