Changes

Implementing logical operator composition with SQL function, making write of "like lower('%a%')" possible.
Adding some new functions : trim, date_format, upper, lower, substring
 (commit: df58e83)

Adding Like.ignoreCase() and Equals.ignoreCase() which introduces BiOperandOperator to be able of specify a function onto the left operand of a conditional operator.
SQLFunction reviewed on its arguments design : values are no more hardcoded as an array and subclass must give value type (can be an Iterable thus). SQLFunction output type is also added to clarify behavior.
Removing ValueWrapper because its more complexity than solves things.
 (commit: 4b5fb19)