Spec is not clear on how to handle this. Three variations exist:
```
$ echo '![text <textarea> text](image.png)' | /home/user/commonmark.js/bin/commonmark
<p><img src="image.png" alt="text <textarea> text" /></p>
$ echo '![text <textarea> text](image.png)' | /home/user/cmark/build/src/cmark
<p><img src="image.png" alt="text <textarea> text" /></p>
$ echo '![text <textarea> text](image.png)' | /home/user/.local/bin/commonmark
<p><img src="image.png" alt="text text" /></p>
```
Prior to this commit:
- when HTML tags are enabled, tags were removed (as in Haskell version)
- when HTML tags are disabled, tags were escaped (as in C version)
After this commit:
- tags will be escaped (as in C version) regardless of HTML flag
+ render hardbreaks as newlines, same as cmark