Merge branch 'rs/strbuf-expand-step'

Code clean-up around strbuf_expand() API. * rs/strbuf-expand-step: strbuf: simplify strbuf_expand_literal_cb() replace strbuf_expand() with strbuf_expand_step() replace strbuf_expand_dict_cb() with strbuf_expand_step() strbuf: factor out strbuf_expand_step() pretty: factor out expand_separator()