history.md: HISTORY_IGNORE docs improvements

I suggest using this syntax for definition list, until the [blocking
problem](pulldown-cmark/pulldown-cmark#67) on the
pulldown-cmark-side is fixed.

manual/src/history.md

@@ -31,13 +31,18 @@ Ideally, this value should be the same as `HISTFILE_SIZE`
 Specifies which commands should **NOT** be saved in the history.
 This is an array and defaults to an **empty array**, meaning that all commands will be saved.
 Each element of the array can take one of the following options:
-- **all** -> All commands are ignored, nothing will be saved in the history.
-- **no_such_command** -> Commands which return `NO_SUCH_COMMAND` will not be saved in the history.
-- **whitespace** -> Commands which start with a [whitespace character](https://doc.rust-lang.org/stable/reference/whitespace.html) will not be saved in the
-history.
-- **regex:xxx** -> Where xxx is treated as a [regular expression](https://doc.rust-lang.org/regex/regex/index.html).
-Commands which match this regular expression will not be saved in the history.
-- **duplicates** -> All preceding duplicate commands are removed/ignored from the history after a matching command is entered.
+- **all** <br/>
+  All commands are ignored, nothing will be saved in the history.
+- **no_such_command** <br/>
+  Commands which return `NO_SUCH_COMMAND` will not be saved in the history.
+- **whitespace** <br/>
+  Commands which start with a [whitespace character](https://doc.rust-lang.org/stable/reference/whitespace.html) will not be saved in the
+  history.
+- **regex:xxx**  <br/>
+  Where xxx is treated as a [regular expression](https://doc.rust-lang.org/regex/regex/index.html).
+  Commands which match this regular expression will not be saved in the history.
+- **duplicates**  <br/>
+  All preceding duplicate commands are removed/ignored from the history after a matching command is entered.
 
 **Notes**
 - You can specify as many elements as you want.