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.cpp b/src/cmdmapper.cpp
index 55f8214..b4d35d4 100644
--- a/src/cmdmapper.cpp
+++ b/src/cmdmapper.cpp
@@ -197,6 +197,8 @@ CommandMap htmlTagMap[] =
   { "blockquote", HTML_BLOCKQUOTE },
   { "strike",     HTML_STRIKE },
   { "u",          HTML_UNDERLINE },
+  { "ins",        HTML_INS },
+  { "del",        HTML_DEL },
 
   { "c",            XML_C },
   // { "code",       XML_CODE },  <= ambiguous <code> is also a HTML tag