Supported nested backquotes

[inexorabletash]

` has special behavior when nested, deferring handling of ,.

Backquotes can be nested. Substitution is done only for commas at the same depth as the backquote in which they are found:

? show `[a `[b ,[1+2] ,[foo ,[1+3] d] e] f]
[a ` [b , [1+2] , [foo 4 d] e] f]

?make "name1 "x
?make "name2 "y
? show `[a `[b ,:,:name1 ,",:name2 d] e]
[a ` [b , [:x] , ["y] d] e]