test: add more PHDU tests
card: FITS-string format of complex differ from go's
phdu: handle int/int64 skew for EXTVER
phdu: handle int/uint cards
phdu: special case strings. take pointer. not address of pointer
test: add TestHeaderRW
phdu: properly pass axes to fits_create_img
image: add explicit handling of []int8 images
image: copy slice into dst instead of replacing it
test: add TestImageRW
table: first stab at Table.Write