Default double_quotes flag should be chars

[ichiban]

#176 (comment)

The current default is codes, which follows GNU Prolog.

prolog/engine/parser.go

Line 628 in f202946

doubleQuotesCodes doubleQuotes = iota

[ichiban]

The ISO standard says the default value is implementation defined.

7.11.2.5 Flag: double-quotes

Possible values: chars, codes, atom

Default value: implementation defined

Changeable: Yes

[guregu]

I like chars as a default. @triska's lesson on DCGs outlines a good argument for using it. Alignment with Scryer and Tau is also nice.
https://www.metalevel.at/prolog/dcg

[ichiban]

Done! This change will be in the next release v0.9.0.

$ go run cmd/1pl/main.go 
?- current_prolog_flag(double_quotes, V).
V = chars.
?- X = "abc".
X = [a, b, c].