Instantiates a new AsciiCodec.
If allowInvalid is true, the decode method and the converter
returned by decoder will default to allowing invalid values.
If allowing invalid values, the values will be decoded into the Unicode
Replacement character (U+FFFD). If not, an exception will be thrown.
Calls to the decode method can choose to override this default.
Encoders will not accept invalid (non Latin-1) characters.
Source
const AsciiCodec({bool allowInvalid: false}) : _allowInvalid = allowInvalid;