v3.1.0. Strict mode. Atomic Records. Robust(er) unicode handling

Unicode support made more robust and encoding bugs fixed

• Truncation of field names and text fields now respects unicode code point boundaries (fixes issues -
  416 and 148).
• Warnings raised if truncation, or replacing b" " with b"_" would corrupt encoded field names, -
  both if they would either be undecodable, or would silently decode to incorrect data (warns users
  if issue 421 applies).
• Correctly truncated field names are now stored in field instances, as would actually be seen in the file.
• New strict mode. Writer(strict=True) raises errors or refuse to create fields and text records with data that -
  would be truncated or cannot be correctly decoded back again by PyShp, exactly as given by the user.
• In strict mode, ascii spaces in encoded names are no longer replaced by ascii underscores at all
  (work around to avoid corrupting unicode field names - provides opt-in fix for issue 421).
• BREAKING. When reading .dbf files, Trailing ascii spaces in text fields before a null terminator char (in the -
  decoded string) is now removed (i.e. instead of .strip().rstrip('\x00') we now do: .rstrip("\x00").rstrip(" ")).
• BREAKING. Enclosing Whitespace other than trailing ascii spaces (0x20) after null chars in text fields is now -
  preserved, when reading .dbf files (fixes issue 418 - James feels this was a bug. Let him know if you think otherwise).
• BREAKING Trailing null chars other than null terminators & null padding bytes, followed by whitespace other than
  ascii spaces, are now preserved.
• Writing dbf records is now atomic.

ShpWriter.shape API Tweak (small breaking change).

• Make ShpWriter.shape return shape length in bytes (the
  same as for offset) not in 16 bit words.

Testing

• Include NullShapes in shp round trip test.
• En/decoding of Dbf files and Fields round trips correctly.