Implementation of a FE matrix assembler.

Main sources:
 assembler2.cc - C++ source for the assembler class
 assembler.mw  - MWrap file describing MATLAB-to-C++ bindings

Timing test:
 timeit.m      - Timing driver for three versions of wathen.m
 wathen_td.m   - Version using MATLAB sparse command
 wathen_db1.m  - Version calling Assembler class for each element
 wathen_db2.m  - Version that makes a batched call to the assembler
