Support for command substitution for the Bash language

Command substitution is a very important part of the Bash
language. Every non trivial script uses it in one way or another.
This patch adds support for it.

components/prism-bash.js

@@ -19,6 +19,13 @@
 					punctuation: /\(\(?|\)\)?|,|;/
 				}
 			},
+			// Command Substitution
+			{
+				pattern: /\$\([^)]+\)|`[^`]+`/,
+				inside: {
+					variable: /^\$\(|^`|\)$|`$/
+				}
+			},
 			/\$(?:[a-z0-9_#\?\*!@]+|\{[^}]+\})/i
 		],
 	};
@@ -61,4 +68,11 @@
 		'operator': /&&?|\|\|?|==?|!=?|<<<?|>>|<=?|>=?|=~/,
 		'punctuation': /\$?\(\(?|\)\)?|\.\.|[{}[\];]/
 	};
+
+	var inside = insideString.variable[1].inside;
+	inside['function'] = Prism.languages.bash['function'];
+	inside.keyword = Prism.languages.bash.keyword;
+	inside.boolean = Prism.languages.bash.boolean;
+	inside.operator = Prism.languages.bash.operator;
+	inside.punctuation = Prism.languages.bash.punctuation;
 })(Prism);

tests/languages/bash/command_substitution_feature.test

@@ -0,0 +1,34 @@
+$(echo foo)
+`echo foo`
+"$(echo foo) bar"
+
+----------------------------------------------------
+
+[
+	["variable", [
+		["variable", "$("],
+		["keyword", "echo"], 
+		" foo",
+		["variable", ")"]
+	]],
+	["variable", [
+		["variable", "`"],
+		["keyword", "echo"], 
+		" foo",
+		["variable", "`"]
+	]],
+	["string", [
+		"\"",
+		["variable", [
+			["variable", "$("],
+			["keyword", "echo"], 
+			" foo",
+			["variable", ")"]
+		]],
+		" bar\""
+	]]
+]
+
+----------------------------------------------------
+
+Checks for command substitution.