ANN: Serpent v0.15; Serializer and pretty-printer with new options

[Paul K <paulclinger@...>]

Serpent is a Lua serializer and pretty printer
(http://notebook.kulchenko.com/programming/serpent-lua-serializer-pretty-printer).
Thanks to all who provided feedback on this maillist and over email;
the recent updates incorporate most of the feedback I received:

- Added `maxlevel` option to limit the depth of processing
- Added `ignore` option to allow ignoring table values.
- Added `comment=num` option to set the max level up to which add comments.
- Fixed several issues with key sorting.
- Removed addresses from names of temporary variables (to generate
more stable output for diffing).

The tests and documentation have been updated. The module is on github
(https://github.com/pkulchenko/serpent).

Paul.