Merge remote-tracking branch 'origin/topic/timw/595-rapidjson'

Tweaks:
    - Small change to the logic for removing quotes around strings.
    - Updated NEWS & COPYING.3rdparty
    - Use of intrusive_ptr for stack-allocated StringVals
    - Little bit of refactoring (I would love to merge the two BuildJSON() functions, too, but that's a larger task)

* origin/topic/timw/595-rapidjson:
  Use the list of files from clang-tidy when searching for unit tests
  Optimize json_escape_utf8 a bit by removing repeated calls to string methods
  Expand unit test for json_escape_utf8 to include all of the strings from the ascii-json-utf8 btest
  GHI-595: Convert from nlohmann/json to rapidjson for performance reasons
  Convert type-checking macros to actual functions

testing/btest/Baseline/scripts.base.frameworks.logging.ascii-double/json.log

@@ -9,11 +9,11 @@
 {"d":0.1234}
 {"d":50000.0}
 {"d":-50000.0}
-{"d":3.14e+15}
-{"d":-3.14e+15}
-{"d":1.79e+308}
-{"d":-1.79e+308}
-{"d":1.23456789e-05}
+{"d":3140000000000000.0}
+{"d":-3140000000000000.0}
+{"d":1.79e308}
+{"d":-1.79e308}
+{"d":0.0000123456789}
 {"d":2.23e-308}
 {"d":-2.23e-308}
 {"d":null}

testing/btest/Baseline/scripts.base.utils.json/output

@@ -2,7 +2,7 @@ true
 123
 -999
 3.14
--1.23456789e+308
+-1.23456789e308
 9e-308
 1480788576.868945
 "-12.0 hrs"