[filter] introduce cjk_minifier

## Motivation

After some study of librime, it seems that the only way that make `extended_charset` usable is to have `table_translator` enabled and `translator/enable_charset_filter` set to `true`.

However, for schemas which depend on `script_translator` indeed can do nothing about this. Though `luna_pinyin` has a `table_translator`, that is for `custom_phrase`.

So, I just added a new filter named `cjk_minifier` to have this job done regardless the translator being used.

## Working Screenshot

Before,

![screen shot 2014-03-31 at 3 42 12 am](https://cloud.githubusercontent.com/assets/251435/2562269/7015c128-b843-11e3-900f-fa4d8b7931ec.png)

After,

![screen shot 2014-03-31 at 3 42 21 am](https://cloud.githubusercontent.com/assets/251435/2562272/759e9fc0-b843-11e3-9802-ca8d065a04ed.png)

## Further Consideration

It might be a really great idea to add a new switch named `extended_charset` for `luna_pinyin`, `double_pinyin_mspy` and etc., just like the one in `canjie5` :-)