csvtk v0.7.0

• fig bug of "stricter field checking" in v0.6.0 and v0.6.1 when using flag -F/--fuzzy-fields

• csvtk pretty and csvtk csv2md: add attention that
  these commands treat the first row as header line and require them to be unique.

• csvtk stat renamed to csvtk stats, old name is still available as an alias.

• csvtk stat2 renamed to csvtk stats2, old name is still available as an alias.

• #13 seamlessly support for data with meta line of separator declaration used by MS Excel, e.g.,

    $ cat names_with_meta.csv
    sep=,
    id,first_name,last_name,username
    11,"Rob","Pike",rob
    2,Ken,Thompson,ken
    ...
  
    $ cat names_with_meta.csv | csvtk filter2 -f '$id > 2'
    sep=,
    id,first_name,last_name,username
    11,Rob,Pike,rob
    4,Robert,Griesemer,gri