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/cmdmapper.h b/src/cmdmapper.h
index 8c49b3f..d670cd4 100644
--- a/src/cmdmapper.h
+++ b/src/cmdmapper.h
@@ -179,6 +179,8 @@ enum HtmlTagType
   HTML_BLOCKQUOTE= 33,
   HTML_STRIKE    = 34,
   HTML_UNDERLINE = 35,
+  HTML_INS       = 36,
+  HTML_DEL       = 37,
 
   XML_CmdMask    = 0x100,