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, 2 insertions, 0 deletions

diff --git a/src/mandocvisitor.cpp b/src/mandocvisitor.cpp
index 5c98c6f..25e56d3 100644
--- a/src/mandocvisitor.cpp
+++ b/src/mandocvisitor.cpp
@@ -137,9 +137,11 @@ void ManDocVisitor::visit(DocStyleChange *s)
       m_firstCol=FALSE;
       break;
     case DocStyleChange::Strike:
+    case DocStyleChange::Del:
       /* not supported */
       break;
     case DocStyleChange::Underline: //underline is shown as emphasis
+    case DocStyleChange::Ins:
       if (s->enable()) m_t << "\\fI";     else m_t << "\\fP";
       m_firstCol=FALSE;
       break;