Add Matlab2017a strings to Matlab lexer (#1048)

Starting with Matlab R2017a you can create strings using double quotes.
This adds support for that.

lib/rouge/lexers/matlab.rb

@@ -58,15 +58,22 @@ def self.builtins
         rule /\d+L/, Num::Integer::Long
         rule /\d+/, Num::Integer
 
-        rule /'(?=(.*'))/, Str::Single, :string
+        rule /'(?=(.*'))/, Str::Single, :chararray
+        rule /"(?=(.*"))/, Str::Double, :string
         rule /'/, Operator
       end
 
-      state :string do
+      state :chararray do
         rule /[^']+/, Str::Single
         rule /''/, Str::Escape
         rule /'/, Str::Single, :pop!
       end
+
+      state :string do
+        rule /[^"]+/, Str::Double
+        rule /""/, Str::Escape
+        rule /"/, Str::Double, :pop!
+      end
     end
   end
 end

spec/visual/samples/matlab

@@ -3,8 +3,11 @@ function zz=sample(aa)
 % some comments
 %%%%%%%%%%%%%%%%%%
 
-x = 'a string';    % some 'ticks' in a comment
-y = 'a string with ''interal'' quotes';
+x = "a string";    % some "ticks" in a comment
+y = "a string with ""interal"" quotes";
+
+x = 'a char array';    % some 'ticks' in a comment
+y = 'a char array with ''interal'' quotes';
 
 for i=1:20
   disp(i);
@@ -18,7 +21,8 @@ c = a .* b ./ a \ ... comment at end of line and continuation
 
 c = a' * b';  % note: these ticks are for transpose, not quotes.
 
-disp('a comment symbol, %, in a string');
+disp("a comment symbol, %, in a string");
+disp('a comment symbol, %, in a char array');
 
 !echo abc % this isn't a comment - it's passed to system command