Changes

*Huge problem with code '''gmm_2stage_estimated.m'''. In line 80, we compute [[''W]] '' by taking the inverse of matrix ''Om''. We keep getting ''W'' as an ill-conditioned matrix, whose entries are infinitely large. There might be a bug in the readjusted code. I will try to catch it by comparing with the original code. If I can't, will try to set up another skype phone call with Chenyu.