Breve 1.2.3 released

[Cliff Wells]

Changelog:

- let() function. Simpler and more flexible than assign()
- fixes to argument passing in Template class
- breve_server installed by setup.py

Also note that Tidy is being deprecated. It's not useful in its current
incarnation as Tidy tends to alter HTML in such a significant way that
it's almost useless for debugging. The option will remain, but a
replacement for tidylib is being developed.

The core Breve 1.2 code seems pretty solid at this point, but expect a
couple more releases involving tools over the next week or so.

Regards,
Cliff