(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/repay.t

@@ -0,0 +1,30 @@
+.TH Command REPAY
+.NA repay "Repay a loan (all or part)"
+.LV Expert
+.SY "repay <LOAN>"
+The repay command is used to repay loans from other countries.
+.s1
+The <LOAN> argument is the number of the loan you are repaying
+and if not included on the command line
+it will be solicited by the program.
+.s1
+You can repay all or part of the loan with this command;
+however beware of letting the loan become overdue --
+the lender may decide to force collection
+(see \*Qinfo collect\*U).
+.s1
+When you repay on a loan a telegram is sent to the lender
+informing her/him of the amount repaid.
+.s1
+.EX repay 12
+.NF
+You presently owe $4515    payment : $2000
+.FI
+or,
+.EX repay 12
+.NF
+You presently owe $4515   payment : $4515
+Congratulations, you've paid off the loan!
+.FI
+.s1
+.SA "collect, consider, ledger, offer, Loans"