Use underlined < and > for long stairs, yellow < and > for ladders

This makes ASCII and Unicode more consistent, and makes long stairs
and ladders look different. Knowing if stairs are long is more
important than knowing if they're ladders.

Suggestion by ESR.
Replace Guidbook.{txt,tex,mn} with asciidoc transcode of the TeX content.

There are a few minor differences to deal with the fact that asciidoc
can't do continuations of labeled items; this required introducing a
table to prevent the dungeon-graphics option description from becoming
an unmanageably huge blob.

Also, some citations of command characters that are punctuation are
now accompanied by their name spelled out in parens; e,g.: ",
(comma)", because command- character literals are now constant width
rather than quoted and have some tendency to disappear when alone.
Update guidebook.asc to the point where it doesn't tell outright lies.

Major changes include: removing a great many configuration options no
longer supported, bringing the command list up to date for nethack4,
documenting the new AC system correctly, describing many (but probably
not all) UI changes, and updating the history/credits section.
Typo fixes.
Text improvements, including listing nethack4 removed gotchas.
Add some dates to the history.
Options documentation is feature-complete.
Complete command list is now documented.
Unusual movement conditions.
Various corrections and additions from #nethack4.
More corrections from #nethack4.
Selection menus are documented.
Reorganize command list.
Fixes from dtsund's proofreading pass.
Replace Guidbook.{txt,tex,mn} with asciidoc transcode of the TeX content.

There are a few minor differences to deal with the fact that asciidoc
can't do continuations of labeled items; this required introducing a
table to prevent the dungeon-graphics option description from becoming
an unmanageably huge blob.

Also, some citations of command characters that are punctuation are
now accompanied by their name spelled out in parens; e,g.: ",
(comma)", because command- character literals are now constant width
rather than quoted and have some tendency to disappear when alone.
Update guidebook.asc to the point where it doesn't tell outright lies.

Major changes include: removing a great many configuration options no
longer supported, bringing the command list up to date for nethack4,
documenting the new AC system correctly, describing many (but probably
not all) UI changes, and updating the history/credits section.
Typo fixes.
Text improvements, including listing nethack4 removed gotchas.
Copyright/license paperwork for ESR's contributions
Merge branch 'nicehack' of gitorious.org:nitrohack/ais523 into nicehack

Conflicts:
	doc/guidebook.asc