allow for year level archive of rules and guidelines

Adjusted `bin/md2html.cfg` to allow for the creation of year level
archive of the rules and guidelines that were in effect when the given
year's content opened for submissions.

We improved `bin/gen-year-index.sh` so that if there exists
a `YYYY/rules.md` rules archive, then `YYYY/rules.html`
will be created.

We improved `bin/gen-year-index.sh` so that if there exists
a `YYYY/guidelines.md` rules archive, then `YYYY/guidelines.html`
will be created.

Changed `bin/gen-year-index.sh` VERSION from "2.0.0 2025-03-13"
to "2.1.0 2025-07-05".

Adjusted `next/rules.md` and `next/guidelines.md` so that when they are
copied as archived copies of rules and guidelines under a YYYY directory,
the internal links do not break.  There are **NO** changes to the readable
contents of the rules and guidelines, only some changes to a few internal links.

Updated `1992/buzzard.2/index.html, `1993/rince/index.html`, and
`2012/omoikane/index.html that were modified by recent commits.

Rebuild sitemap due to the changes above.

Ran `make www` to test and perform the above.

next/rules.md

@@ -132,9 +132,9 @@ FAQ on "[obtaining and compiling the mkiocccentry tools](../faq.html#mkiocccentr
 and the
 FAQ on "[how to enter the IOCCC](../quick-start.html#enter)"
 as that FAQ has important details on
-[how to register](register.html)
+[how to register](../next/register.html)
 as well as
-[how to upload your submission](submit.html) to the IOCCC.
+[how to upload your submission](../next/submit.html) to the IOCCC.
 </p>
 
 
@@ -312,8 +312,8 @@ Jump to: [top](#)
 </div>
 
 <p class="leftbar">
-You must [register](register.html) in order to submit your entry to the IOCCC.
-You may [register](register.html) while the contest is either
+You must [register](../next/register.html) in order to submit your entry to the IOCCC.
+You may [register](../next/register.html) while the contest is either
 **[pending](../faq.html#pending)** or  **[open](../faq.html#open)**.
 </p>
 
@@ -325,7 +325,7 @@ perhaps as much as a few days, for your registration to be processed and for tha
 </p>
 
 <p class="leftbar">
-Those who [register](register.html) while the contest status is **[pending](../faq.html#pending)**
+Those who [register](../next/register.html) while the contest status is **[pending](../faq.html#pending)**
 will receive their email (containing their [submit server](https://submit.ioccc.org) **Username**
 and **Initial password**), later: usually a few days around the time when the contest status
 becomes **[open](../faq.html#open)**.
@@ -333,7 +333,7 @@ becomes **[open](../faq.html#open)**.
 
 <p class="leftbar">
 Once that email with your **Username** and **Initial password** is sent, you
-will have fortnight (**14 days**) to [change your submit server initial password](pw-change.html).
+will have fortnight (**14 days**) to [change your submit server initial password](../next/pw-change.html).
 </p>
 
 <p class="leftbar">
@@ -514,7 +514,7 @@ while the contest is **[open](../faq.html#open)**.
 </p>
 
 <p class="leftbar">
-If you have [registered](register.html) and received by email your [submit
+If you have [registered](../next/register.html) and received by email your [submit
 server](https://submit.ioccc.org) **Username** and **Initial password** you may
 upload your submission to the [submit server](https://submit.ioccc.org) but
 **ONLY** while the contest is **[open](../faq.html#open)**.
@@ -1141,9 +1141,9 @@ FAQ on "[obtaining, compiling, installing and using the mkiocccentry tools](../f
 and the
 FAQ on "[how to enter the IOCCC](../quick-start.html#enter)"
 as that FAQ has important details on
-[how to register](register.html)
+[how to register](../next/register.html)
 as well as
-[how to upload your submission](submit.html) for the IOCCC.
+[how to upload your submission](../next/submit.html) for the IOCCC.
 </p>