csvtk v0.3.8

• new feature: csvtk cut supports ordered fields output. e.g., csvtk cut -f 2,1
  outputs the 2nd column in front of the 1th column.
• new commands: csvtk plot can plot three types of plots by subcommands:
  • csvtk plot hist: histogram
  • csvtk plot box: boxplot
  • csvtk plot line: line plot