Focusing on fulltext search of PostgreSQL

Now we are focusing on the fulltext search function. There is a fulltext search engine for The PostgreSQL named 'senna' in Japan.

We can use it in other languages. So after evaluating the function, I'll write here about it.

In order to evaluate it, I have to add compiler support for '@@' operator. The '@@' operator means fulltext search. The usage is simular to one of the 'like' expression.