A optimized version of normalize function in C.

A optimized version of normalize function in C.
In preivous version of normalize function. The norm2_getInstance function
is being called each time calls the normalize function. This function will
read in some really large file to memory which will be a huge consumption in
 time. In the new implementation, this function is moved to a PG_fini
 function which will be called when the extension's shared library is loading
into the memory. In this way, the initialized normalizer will could be shared
as a global variable instead of loading it in each normalize operation.
Besides it, some of unneccessary memory allocation function is also removed.
Signed-off-by: Swenyu Duan <dsy@sina.com>