Handle quoting U+0000 properly

[bzz]

Fixes #62

TODOs

• add high-level fixtures to reproduce Parsing fails on valid JS: string literal with \0 #62
• add low-level unit test to reproduce the cause - strconv_test.go
• make TestUnquoteSingle pass:
  modify unquoteSingle, so \0 is handled like escape sequence, resulting in U+0000
• make TestUnquoteSingleAndQuoteBack pass:
  modify quoteSingle so U+0000 is handled like in JS and results in \0 (instead of Go \x00)
  That is not possible as right now we are loosing information of the type of escape sequence being used in JS (\000, \x00, and \0 - all end up quoted back in Hex format)
  Instead, test fixtures are update to use this canonical form.

[bzz]

Perf test for comparison of 2 impl of unquoting \0 by replacing it with \x00

go test -bench=. ./driver/normalizer
goos: darwin
goarch: amd64
pkg: github.com/bblfsh/javascript-driver/driver/normalizer
BenchmarkReplacingNullEscape_Iterative-4   	 5000000	       303 ns/op	      80 B/op	       2 allocs/op
BenchmarkReplacingNullEscape_Regexp-4      	 1000000	      1089 ns/op	     168 B/op	       7 allocs/op
PASS
ok  	github.com/bblfsh/javascript-driver/driver/normalizer	2.977s

[bzz]

WIP, but is already open for a feedback

[bzz]

Here are the updated benchmark, including simpler impl suggested in #64 (comment)

goos: darwin
goarch: amd64
pkg: github.com/bblfsh/javascript-driver/driver/normalizer
BenchmarkReplacingNullEscape_Iterative-4   	 2000000	       745 ns/op	     144 B/op	       8 allocs/op
BenchmarkReplacingNullEscape_Regexp-4      	  500000	      3334 ns/op	     480 B/op	      27 allocs/op
BenchmarkReplacingNullEscape_Simple-4      	 2000000	       633 ns/op	     112 B/op	       9 allocs/op
PASS
ok  	github.com/bblfsh/javascript-driver/driver/normalizer	5.897s

It is not just simpler, but is even a bit faster! 👏

[bzz]

All feedback addressed, ready for another round.

[creachadair]

A few minor cosmetic comments, otherwise looks good to me!

Thanks!

[dennwc]

Tests need some changes :)

[bzz]

@creachadair @dennwc thank you very much for thorough and prompt reviews! All feedback addressed, ready for another round.

[creachadair]

One more suggestion on the comment, but I think this is in good shape.
Thanks for your patience!

[dennwc]

LGTM, only one small change remains.

[bzz]

🎉 merging as soon as CI is green.

Thank you everyone for your kind reviews!