Support style and identifier lists in escaped strings.

Example:

  .foo {
    transition: ~"border-color ease-in-out .15s,
                  box-shadow ease-in-out .15s";
  }

lesscpy/lessc/lexer.py

@@ -174,6 +174,15 @@ class LessLexer:
         r'@\{[^@\}]+\}'
         return t
 
+    def t_iselector_t_eclose(self, t):
+        r'"|\''
+        # Can only happen if iselector state is on top of estring state.
+        #
+        # Example: @item: ~".col-xs-@{index}";
+        #
+        t.lexer.pop_state()
+        return t
+
     def t_iselector_css_filter(self, t):
         (r'\[[^\]]*\]'
          '|(not|lang|nth-[a-z\-]+)\(.+\)'

lesscpy/lessc/parser.py

@@ -664,7 +664,8 @@ class LessParser(object):
 #
 
     def p_escaped_string(self, p):
-        """ estring                 : t_eopen style t_eclose
+        """ estring                 : t_eopen style_list t_eclose
+                                    | t_eopen identifier_list t_eclose
         """
         p[0] = p[2]