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.

2019/mills/README.md

@@ -412,7 +412,6 @@ performance, at the cost of a much larger parameter space.
 
 **IMPORTANT NOTE**:
 
-```
 Since OMLET uses the system stack for network storage,
 larger networks may cause OMLET to crash (typically with a message like
 Segmentation fault) unless the system stack size is first increased.
@@ -422,7 +421,6 @@ with ulimit -Hs and set it with ulimit -s 65532 (replacing 65532
 with the actual hard limit).  On csh/tcsh shells, you can view
 the hard limit with limit -h stacksize and set it with
 limit stacksize 65532 (replacing 65532 with the actual hard limit).
-```
 
 <hr style="width:10%;text-align:left;margin-left:0">
 

2019/mills/index.html

@@ -686,15 +686,15 @@ parameters and its own hidden state vector. This will improve the network’s
 performance, at the cost of a much larger parameter space.</p>
 <hr style="width:10%;text-align:left;margin-left:0">
 <p><strong>IMPORTANT NOTE</strong>:</p>
-<pre><code>Since OMLET uses the system stack for network storage,
+<p>Since OMLET uses the system stack for network storage,
 larger networks may cause OMLET to crash (typically with a message like
 Segmentation fault) unless the system stack size is first increased.
-The exact command for doing so depends on your shell and your system&#39;s
-hard limits.  On sh/ksh/bash shells, you can view the hard limit
+The exact command for doing so depends on your shell and your system’s
+hard limits. On sh/ksh/bash shells, you can view the hard limit
 with ulimit -Hs and set it with ulimit -s 65532 (replacing 65532
-with the actual hard limit).  On csh/tcsh shells, you can view
+with the actual hard limit). On csh/tcsh shells, you can view
 the hard limit with limit -h stacksize and set it with
-limit stacksize 65532 (replacing 65532 with the actual hard limit).</code></pre>
+limit stacksize 65532 (replacing 65532 with the actual hard limit).</p>
 <hr style="width:10%;text-align:left;margin-left:0">
 <p>You can try the deeper network by doing</p>
 <pre><code>    make rnn2</code></pre>