use compare function instead of implementing __cmp__
replace all hardcoded int type size with struct.calcsize and fix bug of using struct.calcsize
add 'Declaration' node
use TypeCompareResult to replace hardcoded type comparing results
add compare for PointerType, fix bug of getIRType of PointerType
fix bug of getIRType of IntType, FloatType, DoubleType and VoidType
implement translate for constant expressions
implement translate for VariableDeclarator