(info, html): Implement.

(all): Depend on info.

Flatten info directory.  This undoes the move to one subdirectory per
chapter, which was done during Empire 2.  The structure doesn't buy us
much, as the info name space is flat, and it complicates makefiles.

Overhaul info.pl:
- It now wants to run in the root of the build tree.
- Information on source files and subjects is now stored in makefiles,
  thus info.pl no longer picks up random junk from the file system.
- Clean up Perl anachronisms, in particular use subroutine arguments and
  results rather than global variables where convenient.
- Change format of diagnostics to the common format used by GNU tools,
  so that Emacs and the like can parse it.
- Catch missing .SA.
- When creating a new subject file, cowardly refuse to overwrite an
  existing file.
- Subject files contain topics sorted by chapter, then by name.  The
  order of chapters used to depend on how Perl sorts hash keys.  Fix
  it.

info/fly.t

@@ -0,0 +1,44 @@
+.TH Command FLY
+.NA fly "Fly planes from sector/ship to sector/ship and bomb or snoop"
+.LV Basic
+.SY "fly <TRANSPORTS> <ESCORTS> <SECT> <PATH|DESTINATION> <COMMODITY>"
+The \*Qfly\*U command is used to move planes and commodities from
+the starting sector(s), and ending up in the target sector.
+.s1
+<TRANSPORTS> represents a list of planes which are to travel
+to the target sector.
+Only planes which are provided with gas, and have sufficient mobility will
+be successfully selected for the mission.
+.s1
+<ESCORTS> represent a list of fighter planes which are capable of escorting
+the transports all the way to the target.
+To be selected, escorts must have fuel and mobility.
+.s1
+<SECT> represents an assembly point, where all of the planes in the
+mission meet before proceeding on to the target sector.
+The assembly point must be owned by you or an ally, or you or an ally
+must have a ship there.  It must not be more than
+four sectors away from any of the planes selected for the mission.
+.s1
+<COMMODITY> is the name of a commodity which is to be carried along
+on all of the planes which have a transport capacity.
+If nothing is specified, then nothing will be carried.
+.s1
+Route is a normal empire path specification. You may also give a 
+destination sector on the command line, or at any time while giving
+the route, and empire will use the best path from the current sector
+to the desired destination sector.
+.s1
+When getting a path interactively, empire will show you the information
+you have (from your bmap) concerning the current area, to help you plot
+your course.
+.s1
+If the transports stray over enemy territory, then they will be
+intercepted and shot at just like any other mission.
+If the destination sector is not an airport, then all planes in
+the mission must have VTOL capability.
+.s1
+Note that a plane must be at least 40% efficient before it can leave
+the ground.
+.s1
+.SA "Plane-types, bomb, paradrop, drop, recon, Mobility, Planes, Transportation"