RC1 - first release candidate

• First release candidate
• functions to_json, read_json and as_def_type available
• specific methods available in the class DataFrameConnec and SeriesConnec
• correspondance between NTVtype and dtype in ntv_pandas.ini
• dtype supported:
  • timedelta64[ns], datetime64[ns]
  • string
  • Floatxx, UIntxx, Intxx, boolean
  • categorical
• NTVtype supported:
  • duration, period
  • datetime, date, time, dat
  • month, year, day, wday, yday, week, hour, minute, second
  • json, string, number, boolean, array, object, null
  • floatxx, uintxx, intxx
  • uri, email, file
  • point, line, polygon, geometry, geojson
  • multipoint, multiline, multipolygon, box, codeolc
  • row, field, tab, ntv