fix non-indented markdown code blocks

We have fixed cases where markdown code blocks were not properly intended.

Updated `markdown.md` to discuss how markdown code blocks should be indented
and how blank lines should follow a markdown code block.

We used this shell script to find problematic code blocks:

```sh
find . -name '*.md' ! -name markdown.md -print | xargs pcregrep -M '^``.*\n[^|`\n \t]'
```

Ran `make www` to perform the above.

bin/README.md

@@ -421,13 +421,13 @@ Form a compressed tarball for an entry.
 Usage:
 
 ``` <!---sh-->
-bin/tar-entry.sh -v 1 YYYY/dir
+    bin/tar-entry.sh -v 1 YYYY/dir
 ```
 
 Suggested usage:
 
 ``` <!---sh-->
-bin/all-run.sh -v 3 bin/tar-entry.sh -v 1 -W
+    bin/all-run.sh -v 3 bin/tar-entry.sh -v 1 -W
 ```
 
 
@@ -438,19 +438,19 @@ Form a compressed tarball for an IOCCC year.
 Usage:
 
 ``` <!---sh-->
-bin/tar-year.sh -v 1 YYYY
+    bin/tar-year.sh -v 1 YYYY
 ```
 
 Suggested usage:
 
 ``` <!---sh-->
-bin/all-years.sh -v 3 bin/tar-year.sh -v 1 -W
+    bin/all-years.sh -v 3 bin/tar-year.sh -v 1 -W
 ```
 
 We recommend that this tool be invoked via the top level `Makefile`:
 
 ``` <!---sh-->
-make form_year_tarball
+    make form_year_tarball
 ```
 
 

bin/index.html

@@ -564,17 +564,17 @@ We sort with lines starting with <code>!</code> fourth.</p>
 <h2 id="tar-entry.sh"><a href="../bin/tar-entry.sh">tar-entry.sh</a></h2>
 <p>Form a compressed tarball for an entry.</p>
 <p>Usage:</p>
-<pre><code>bin/tar-entry.sh -v 1 YYYY/dir</code></pre>
+<pre><code>    bin/tar-entry.sh -v 1 YYYY/dir</code></pre>
 <p>Suggested usage:</p>
-<pre><code>bin/all-run.sh -v 3 bin/tar-entry.sh -v 1 -W</code></pre>
+<pre><code>    bin/all-run.sh -v 3 bin/tar-entry.sh -v 1 -W</code></pre>
 <h2 id="tar-year.sh"><a href="../bin/tar-year.sh">tar-year.sh</a></h2>
 <p>Form a compressed tarball for an IOCCC year.</p>
 <p>Usage:</p>
-<pre><code>bin/tar-year.sh -v 1 YYYY</code></pre>
+<pre><code>    bin/tar-year.sh -v 1 YYYY</code></pre>
 <p>Suggested usage:</p>
-<pre><code>bin/all-years.sh -v 3 bin/tar-year.sh -v 1 -W</code></pre>
+<pre><code>    bin/all-years.sh -v 3 bin/tar-year.sh -v 1 -W</code></pre>
 <p>We recommend that this tool be invoked via the top level <code>Makefile</code>:</p>
-<pre><code>make form_year_tarball</code></pre>
+<pre><code>    make form_year_tarball</code></pre>
 <h2 id="untar-entry.sh"><a href="../bin/untar-entry.sh">untar-entry.sh</a></h2>
 <p>Untar an entry’s a compressed tarball.</p>
 <p>Usage:</p>