Adding HTML tags ins and del

Github does not support the `<u>` tag for underlined text, in HTML there exists the tag `<ins>`. On https://www.w3schools.com/tags/tag_ins.asp is written:
The `<ins>` tag defines a text that has been inserted into a document.
Browsers will normally strike a line through deleted text and underline inserted text.

Most browsers will display the `<ins>` element with the following default values:
```
ins {
  text-decoration: underline;
}
```

analogous there exists the tag `<del>` (https://www.w3schools.com/tags/tag_del.asp):
The `<del>` tag defines text that has been deleted from a document.
Browsers will normally strike a line through deleted text and underline inserted text.

Most browsers will display the `<del>` element with the following default values:
```
del {
  text-decoration: line-through;
}
```

Definitions analogue to the underline and strike through tag the implementation for the other formats has been chosen.

1 files changed, 17 insertions, 0 deletions

diff --git a/testing/086_style_tags.h b/testing/086_style_tags.h
new file mode 100644
index 0000000..105adca
--- /dev/null
+++ b/testing/086_style_tags.h
@@ -0,0 +1,17 @@
+// objective: test different HTML style tags
+// check: 086__style__tags_8h.xml
+/**
+\file
+
+In the following the word tag has the style as indicated before it.
+- This is a bold <b>tag</b>.
+- This is a `strong` bold <strong>tag</strong>.
+- This is an italic <i>tag</i>.
+- This is an `em` italic <em>tag</em>.
+- This is a strike through <strike>tag</strike>.
+- This is an underline <u>tag</u>.
+- This is an insterted <ins>tag</ins>.
+- This is a deleted <del>tag</del>.
+- This is a typewriter <tt>tag</tt>.
+*/
+