edify extensions for OTA package installation, part 1

Adds the following edify functions:

  mount unmount format show_progress delete delete_recursive
  package_extract symlink set_perm set_perm_recursive

This set is enough to extract and install the system part of a (full)
OTA package.

Adds the updater binary that extracts an edify script from the OTA
package and then executes it.  Minor changes to the edify core (adds a
sleep() builtin for debugging, adds "." to the set of characters that
can appear in an unquoted string).
diff --git a/edify/README b/edify/README
index 5ccb582..810455c 100644
--- a/edify/README
+++ b/edify/README
@@ -10,7 +10,7 @@
   understood, as are hexadecimal escapes like \x4a.
 
 - String literals consisting of only letters, numbers, colons,
-  underscores, and slashes don't need to be in double quotes.
+  underscores, slashes, and periods don't need to be in double quotes.
 
 - The following words are reserved: