Update NEWS.

* NEWS: Mention Emacs interface for Hydra and changes in variables.

NEWS

@@ -10,6 +10,37 @@ Copyright © 2013, 2014, 2015 Ludovic Courtès <ludo@gnu.org>
 
 Please send Guix bug reports to bug-guix@gnu.org.
 
+* Changes in 0.9.1 (since 0.9.0)
+
+** Package management
+
+*** Emacs interface for hydra.gnu.org
+*** Changes in Emacs interface variables
+In the following names, BUFFER-TYPE means "info" or "list";
+ENTRY-TYPE means "package", "output" or "generation".
+
+**** Removed
+- guix-info-fill-column
+- guix-info-insert-ENTRY-TYPE-function
+
+**** Renamed
+- guix-info-ignore-empty-vals -> guix-info-ignore-empty-values
+- guix-output-name-width -> guix-generation-output-name-width
+- guix-buffer-name-function -> guix-ui-buffer-name-function
+- guix-update-after-operation -> guix-ui-update-after-operation
+- guix-search-params -> guix-package-search-params
+
+**** Replaced
+- guix-list-column-format, guix-list-column-value-methods ->
+  guix-ENTRY-TYPE-list-format
+- guix-info-displayed-params, guix-info-insert-methods,
+  guix-package-info-heading-params -> guix-ENTRY-TYPE-info-format
+- guix-param-titles, guix-list-column-titles ->
+  guix-ENTRY-TYPE-BUFFER-TYPE-titles
+- guix-list-describe-warning-count ->
+  guix-ENTRY-TYPE-list-describe-warning-count
+- guix-package-info-fill-heading -> guix-info-fill
+
 * Changes in 0.9.0 (since 0.8.3)
 
 ** Package management