(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/llookout.t

@@ -0,0 +1,37 @@
+.TH Command LLOOKOUT
+.NA llookout "Check from units for other units, planes and/or sector types"
+.LV Basic
+.SY "lookout <UNIT/ARMY>"
+The lookout command allows units to report sightings
+of other units, planes, and land sectors.
+.s1
+Note that non-spy units require military on-board in order to be able
+to see anything.
+.s1
+The various ranges over which lookout is effective
+break down into two groups:
+.s1
+UNIT to UNIT
+.s1
+.in +0.2i
+This range is dependent on both the visibility of the unit
+being observed and the visual range of the observing unit.
+(see \*Qinfo Unit-types\*U)
+.in
+.s1
+UNIT to PLANE
+.s1
+.in +0.2i
+Planes are treated as if they had a visibility of 10.
+.in
+.s1
+For example:
+.EX lookout 24
+.NF
+Groonland (#2) jf4 jet fighter 4 #3 @2,-2
+Groonland (#2) airfield 100% efficient with approx 50 civ @ 2,-2
+Groonland (#2) highway 20% efficient with approx 20 civ @ 3,-1
+Groonland (#2) highway 0% efficient with approx 0 civ @ 0,-2
+.FI
+.s1
+.SA "lookout, coastwatch, Unit-types, Sector-types, radar, sonar, LandUnits, Detection"