Add support dereferencing with block

[usualoma]

Hi,

This pull request contains adding support dereferencing with block.
https://metacpan.org/pod/perlref#Block

We can use the following syntax to dereference.

print ${\"string"};
print @{[lc("STRING")]};
print %{{1 => 2}};
print &{sub{ "sub" }};

This syntax is often used to embed expressions in strings.
https://github.com/leejo/CGI.pm/blob/master/lib/CGI.pm#L3638

19974bc makes match a code block, for example, as in the following JavaScript plist.
https://github.com/textmate/javascript.tmbundle/blob/master/Syntaxes/JavaScript.plist#L1047-L1075

Then, 5e87c64 handles dereferencing.

And the following syntax is a pattern of dereferencing with block, so I think we can also add the following changes.

${$variable};

diff --git a/Syntaxes/Perl.plist b/Syntaxes/Perl.plist
index cfc22d9..4ac01e8 100644
--- a/Syntaxes/Perl.plist
+++ b/Syntaxes/Perl.plist
@@ -4587,7 +4587,7 @@
 						</dict>
 					</dict>
 					<key>match</key>
-					<string>(\$\{)(?:[a-zA-Zx7f-xff\$]|::)(?:[a-zA-Z0-9_x7f-xff\$]|::)*(\})</string>
+					<string>(\$\{)(?:[a-zA-Zx7f-xff]|::)(?:[a-zA-Z0-9_x7f-xff]|::)*(\})</string>
 					<key>name</key>
 					<string>variable.other.readwrite.global.perl</string>
 				</dict>

Kind regards,

[oalders]

@usualoma could you add a graphic which shows the various cases before and after your changes?