slog: remove attempted subheading markers

go/doc/comment does not recognize subheadings. Remove the "##" prefix
from such headings.

As suggested in https://go.dev/doc/comment, end each subheading line with
a period to defeat gofmt's attempt to prefix those lines with a "#".

Change-Id: Idfd4328d6a8a6441838990175d2dbb0da2fa2bf7
Reviewed-on: https://go-review.googlesource.com/c/exp/+/476199
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>

slog/doc.go

diff --git a/slog/doc.go b/slog/doc.go
index 40430cc..7b9133f 100644
--- a/slog/doc.go
+++ b/slog/doc.go
@@ -214,7 +214,7 @@
 
 # Advanced topics
 
-## Customizing a type's logging behavior
+Customizing a type's logging behavior.
 
 If a type implements the [LogValuer] interface, the [Value] returned from its LogValue
 method is used for logging. You can use this to control how values of the type
@@ -226,7 +226,7 @@
 method handles these cases carefully, avoiding infinite loops and unbounded recursion.
 Handler authors and others may wish to use Value.Resolve instead of calling LogValue directly.
 
-## Wrapping output methods
+Wrapping output methods.
 
 The logger functions use reflection over the call stack to find the file name
 and line number of the logging call within the application. This can produce
@@ -248,7 +248,7 @@
 The Infof function in the package-level example called "wrapping"
 demonstrates how to do this.
 
-## Working with Records
+Working with Records.
 
 Sometimes a Handler will need to modify a Record
 before passing it on to another Handler or backend.
@@ -262,7 +262,7 @@
 or create a new Record with [NewRecord]
 and build up its Attrs by traversing the old ones with [Record.Attrs].
 
-## Performance considerations
+Performance considerations.
 
 If profiling your application demonstrates that logging is taking significant time,
 the following suggestions may help.