使用magrittr的tee操作符（％T>％）将pando

@andrewheiss 整洁#rstats tidyverse技巧：使用magrittr的tee操作符（％T>％）将pandoc表输出到文档中（如在Rmd块中）并将表保存到文件中，而无需创建中间对象

library(tidyverse)
library(pander)
mtcars %>%
  group_by(cyl, gear) %>%
  summarize(avg_mpg = mean(mpg), avg_hp = mean(hp)) %T>% # tee operator
  pandoc.table() %>% # Print the output
  pandoc.table.return() %>% # Save the output
  cat(file = "output.md")