csvtk v0.14.0

Changelog

• csvtk: supporting multi-line fields by replacing multicorecsv with standard library encoding/csv,
  while losing support for metaline which was supported since v0.7.0. It also gain a little speedup.
• csvtk sample: add flag -n/--line-number to print line number as the first column ("n")
• csvtk filter2: fix bug when column names start with digits, e.g., 1000g2015aug (#44)
• csvtk rename2: add support for similar repalecement symbols {kv} and {nr} in csvtk replace