clang-tidy fixes again (#1087)

* [clang-tidy] Do not use else after return

Found with readability-else-after-return

Signed-off-by: Rosen Penev <rosenp@gmail.com>

* [clang-tidy] Convert several loops to be range based

Found with modernize-loop-convert

Signed-off-by: Rosen Penev <rosenp@gmail.com>

* [clang-tidy] Replace deprecated C headers

Found with modernize-deprecated-headers

Signed-off-by: Rosen Penev <rosenp@gmail.com>

* [clang-tidy] Use auto where applicable

Found with modernize-use-auto

Signed-off-by: Rosen Penev <rosenp@gmail.com>

* .clang-tidy: Add these checks
diff --git a/src/jsontestrunner/main.cpp b/src/jsontestrunner/main.cpp
index f6b1a4d..cdf6bff 100644
--- a/src/jsontestrunner/main.cpp
+++ b/src/jsontestrunner/main.cpp
@@ -57,10 +57,10 @@
   if (!file)
     return "";
   fseek(file, 0, SEEK_END);
-  long const size = ftell(file);
-  const auto usize = static_cast<size_t>(size);
+  auto const size = ftell(file);
+  auto const usize = static_cast<size_t>(size);
   fseek(file, 0, SEEK_SET);
-  char* buffer = new char[size + 1];
+  auto buffer = new char[size + 1];
   buffer[size] = 0;
   Json::String text;
   if (fread(buffer, 1, usize, file) == usize)