(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/Nuke-types.t

@@ -0,0 +1,79 @@
+.TH Concept "Nuke Types"
+.NA Nuke-types "Description of different kinds of nuclear weapons"
+.LV Expert
+There are two different types of nuclear devices in Empire:
+fission bombs, fusion bombs.
+Both fission and fusion bombs perform similarly,
+with fusion bombs giving \*Qmore bang for the buck\*U.
+.s1
+In general, the only way to avoid damage by a nuclear detonation
+is to avoid the area prior to and during actual detonation.
+\*QHardening\*U missiles (in silos) is the only exception,
+and even that cannot protect from a direct hit
+by the larger nuclear devices.
+.s1
+The details of the nuclear devices present in Empire can be seen using
+the show command.
+The meaning of the fields are as follows:
+.s1
+.in \w'name\0\0'u
+.L name
+The nukes name.
+.L lcm
+The amount of lcm needed to build the nuke
+.L hcm
+The amount of hcm needed to build the nuke
+.L oil
+The amount of crude oil required to build it.
+.L rad
+The number of radioactive products required to build it.
+.L tech
+The minimum tech level required to construct the nuke.
+.L $
+The cost of the nuke to construct.
+.s1
+.in
+The other fields given in the capabilities are as follows.
+.s1
+.in \w'blst\0\0'u
+.L blst
+The blast type of the nuke
+.L dam
+The damage rating of the nuke
+.L lbs
+the weight of the warhead, limiting missile and plane nuclear
+device carrying capacity.
+.in
+.s1
+As a guide (these numbers are subject to change):
+.EX show nuke build
+.NF
+        lcm hcm  oil  rad tech $
+10kt fission   50  50   25   50  200 $7500
+50kt fission   60  60   30   75  225 $9000
+100kt fission  75  75   40  100  250 $12000
+250kt fusion   50  50   25   50  280 $7500
+500kt fusion   60  60   30   75  295 $9000
+1mt fusion     75  75   50  100  310 $12000
+3mt fusion    100 100   75  127  325 $19000
+.FI
+.s1
+.EX show nuke capab
+.NF
+        blst dam lbs tech $
+10kt fission     3  80   4  200 $7500
+50kt fission     3 100   6  225 $9000
+100kt fission    4 120   8  250 $12000
+250kt fusion     4 150   4  280 $7500
+500kt fusion     5 170   6  295 $9000
+1mt fusion       6 190   8  310 $12000
+3mt fusion       7 210  10  325 $19000
+.FI
+.s1
+The larger the megatonnage, the more damage done by the weapon.
+Effects (as in the real world) can only be determined
+by experimentation,
+although research suggests that radioactivity left behind by nuclear
+detonations may have lasting effects.
+.s1
+.SA "launch, fly, build, transport, show, Planes"