Change neo* configurations to n* configurations
Extract pos.h from structs.h

This will make it much simpler to move the other types in structs.h
which depend on `pos_T` and `lpos_T`.
Move exarg_T and cmdarg_T from structs.h to normal.h
Extract cursor_shape.c from misc2.c and types/consts from structs.h
Remove CURSOR_SHAPE #ifdef tests

See issue #333