Dmitry Vyukov 18847f55bb pkg/ast: introduce hex-encoded string literals
The stringnozescapes does not make sense with filename,
also we may need similar escaping for string flags.
Handle escaped strings on ast level instead.
This avoids introducing new type and works seamleassly with flags.

As alternative I've also tried using strconv.Quote/Unquote
but it leads to ugly half-escaped strings:
"\xb0\x80s\xe8\xd4N\x91\xe3ڒ,\"C\x82D\xbb\x88\\i\xe2i\xc8\xe9\xd85\xb1\x14):M\xdcn"

Make hex-encoded strings a separate string format instead.
2020-02-10 14:45:20 +01:00
..
2018-01-11 11:45:35 +01:00
2018-03-08 18:48:26 +01:00
2019-10-23 10:22:35 +02:00