guix-packages: Move to "ambrevar" subfolder

This is useful to make it clear where those packages come from.

.config/guix/config.scm

@@ -7,7 +7,7 @@
 
 (use-modules (gnu)
              (gnu packages linux)
-             (linux-custom)             ; TODO: Move to "ambrevar" namespace.
+             (ambrevar linux-custom)
              (gnu packages tls)
              (gnu system nss)
              (guix build-system trivial)

.guix-packages/ambrevar/linux-custom.scm

@@ -1,4 +1,4 @@
-(define-module (linux-custom)
+(define-module (ambrevar linux-custom)
   #:use-module (guix gexp)
   #:use-module (guix packages)
   #:use-module (guix download)

.guix-packages/ambrevar/unrar.scm

@@ -1,4 +1,4 @@
-(define-module (unrar)
+(define-module (ambrevar unrar)
   #:use-module (guix licenses)
   #:use-module (guix packages)
   #:use-module (guix build-system gnu)