Implements Session Parameters.

A SessionParam is a parameter that can modify MDX and SQL queries. The parameters are held in a SessionParamPool. There is one pool per HttpSession.

SessionParam may be created in several ways:

Parameters may be used in sql queries. Example for JSTL's sql tag:
<jsp:useBean id="paramPool" class="com.tonbeller.jpivot.param.SessionParamPool" scope="session"/>

<sql:query var="result" dataSource="${myDataSource}">
  SELECT ...
  FROM ...
  WHERE CUSTOMERID = ?
  <sql:param value="${paramPool.CUSTOMERID.sqlValue}"/>
</sql:query>