Implement visible option for Page.waitFor method

This patch adds a 'visible' option to the Page.waitFor method, making
it possible to wait for the element to become actually visible.

References #89, #91.

utils/doclint/test/04-bad-arguments/doc.md

@@ -3,5 +3,5 @@
 - `arg1` <[string]>
 - `arg2` <[string]>
 
-#### foo.test(fileNames)
-- `filePaths` <[Array]>
+#### foo.test(...files)
+- `...filePaths` <[string]>

utils/doclint/test/04-bad-arguments/foo.js

@@ -1,7 +1,7 @@
 class Foo {
-  constructor(arg1, arg3) {
+  constructor(arg1, arg3 = {}) {
   }
 
-  test(filePaths) {
+  test(...filePaths) {
   }
 }

utils/doclint/test/golden/04-bad-arguments.txt

@@ -1,4 +1,4 @@
 [MarkDown] Method Foo.constructor() fails to describe its parameters:
 - Argument not found: arg3
 - Non-existing argument found: arg2
-[MarkDown] Heading arguments for "foo.test(fileNames)" do not match described ones, i.e. "fileNames" != "filePaths"
+[MarkDown] Heading arguments for "foo.test(...files)" do not match described ones, i.e. "...files" != "...filePaths"