Added custom caching functions

This is a combination of 20 commits:
added cache callback #212

added test

Added text for custom cache

formating and tests

added caching_auto_clear option

moved custom cache test for php 5.3+

fixed ConfigTest.php

tabs to spaces

formating

formating

added `create_cache_key` callback option

added $table_name to clear cache function

added $table_name to _create_cache_key

added missing params

added $table_name to cache_query_result

formating

tabs

added $table_name to check_query_cache

unify cache parameters order

`table_name` is more important than `connection_name`

formating
Tidy up the caching pull request
Document project status