Move everything to src directory

src/spm_read_driver.c

src/z_spm.c

src/z_spm.h

src/z_spm_2dense.c

src/z_spm_convert_to_csc.c

src/z_spm_convert_to_csr.c

src/z_spm_convert_to_ijv.c

src/z_spm_dof_extend.c

src/z_spm_expand.c

src/z_spm_genrhs.c

src/z_spm_integer.c

src/z_spm_laplacian.c

src/z_spm_matrixvector.c

src/z_spm_norm.c

src/z_spm_print.c

src/z_spm_scal.c