replace <outp> command with \outp in docs

Doxygen has been warning that `<outp>` and `</outp>` are not valid XML/HTML commands since commit cb6d5d76 on 20016-04-04. That's primarily because there is at present no way to tell Doxygen to recognize new XML/HTML tags. The actual errors look like this:

```
.../string.doxygen:187: warning: Unsupported xml/html tag </outp> found
```

I hate build errors since they a) cause needless concern, and b) make it harder to notice when I've introduced a new error. So switch from XML/C## style markup to Doxygen style markup for the "outp" annotation.

1 files changed, 2 insertions, 2 deletions

diff --git a/doc_src/FORMATTING.md b/doc_src/FORMATTING.md
index df6de6f8..4b4b2338 100644
--- a/doc_src/FORMATTING.md
+++ b/doc_src/FORMATTING.md
@@ -158,10 +158,10 @@ The following can be used in \\fish blocks to render some fish scenarios. These
 - `<m>`: \<m\>Matched\</m\> items, such as tab completions.
 - `<sm>`: Matched items \<sm\>searched\<sm\> for, like grep results.
 - `<error>`: \<error\>This would be shown as an error.\</error\>
-- `<asis>`: \<asis\>This test will not be parsed for fish markup.\</asis\>
-- `<outp>`: \<outp\>This would be rendered as command/script output.\</outp\>
+- `<asis>`: \<asis\>This text will not be parsed for fish markup.\</asis\>
 - `<bs>`: Render the contents with a preceding backslash. Useful when presenting output.
 - `{{` and `}}`: Required when wanting curly braces in regular expression example.
+- `\\outp`: \\outp\{This would be rendered as command/script output.\}
 
 ### Prompts and cursors