Add support for alternative implementations of an HTS engine

All implementations derive from an abstract base class. They are only
responsible for the synthesis itself, unlike the old implementation,
which included a lot of unrelated code. The steps which don't depend
on the engine are represented by separate classes. So, the user can
now choose between two implementations: the standard one using the HTS
engine developed by the HTS working group, and the implementation
using Mage for parameter generation, which should respond more quickly
on long sentences.
In the process of this rewrite we have changed the way possible
post-processing can be applied to the synthesized speech before it is
passed to the client. Each post-processing action is represented by a
class and they are organized in a chain. At run-time we decide which
post-processors should be included in the chain. So it is possible to
plug in such things as filters, if the user requests it.
A small change in the Russian phoneset
A set of Russian prompts corrected according to what a new speaker,
Anna, actually said
Fix the sentence selection script

* Add an ability to ignore case.
* Use minimum word frequency to decide which words to consider common enough.
A few fixes for the training data preparation script
Add an internal voice setting which defines the default volume of the
voice

This should help to reduce volume difference between voices.
Fix compilation under Windows
Start working on a new packaging scheme

Voices and languages should be packaged separately. This way we will
be able to update each of them independently, and the users will not
have to download components they don't need.
A script for generating the initial version of the function/content
word classifier for a new language.

It uses wiktionary to get lists of function words. It's just a
temporary solution, until we can get more information about the
language from some other source.
A script which generates the initial versions of the classes
implementing support for a new language.

Each time we have to type basically the same code, so it makes sense
to automate the process.
Fix the data preparation script to work with the version of ehmm from
the latest publically available version of festvox
Set default HTS engine implementation to Mage
New Russian female voice
Fix a typo
Implement initial support for the Georgian language
Fix Mage (properly this time), so it builds and works on Windows
Almost finish the implementation of the new packaging scheme for Windows