Fix a parser bug where tokens are misidentified as commas. (#1502)

* Fix a parser bug where tokens are misidentified as commas.

In the old and new readers, when parsing an object, a comment
followed by any non-`}` token is treated as a comma.

The new unit test required changing the runjsontests.py
flag regime so that failure tests could be run with default settings.

* Honor allowComments==false mode.

Much of the comment handling in the parsers is bespoke, and does not
honor this flag.  By unfiying it under a common API, the parser is
simplified and strict mode is now more correctly strict.

Note that allowComments mode does not allow for comments in
arbitrary locations; they are allowed only in certain positions.
Rectifying this is a bigger effort, since collectComments mode requires
storing the comments somewhere, and it's not immediately clear
where in the DOM all such comments should live.

---------

Co-authored-by: Jordan Bayles <bayles.jordan@gmail.com>

test/data/fail_strict_comment_01.json

@@ -0,0 +1,4 @@
+{
+  "a": "aaa",
+  "b": "bbb" // comments not allowed in strict mode
+}

test/data/fail_strict_comment_02.json

@@ -0,0 +1,4 @@
+{
+  "a": "aaa", // comments not allowed in strict mode
+  "b": "bbb"
+}

test/data/fail_strict_comment_03.json

@@ -0,0 +1,3 @@
+{
+  "array" : [1, 2, 3 /* comments not allowed in strict mode */]
+}

test/data/fail_test_object_02.json

@@ -0,0 +1 @@
+{"one": 1 /* } */ { "two" : 2 }