Reduce the header declarations (#1342)

- Since we have style rules to include foo.hpp at the top of its
  corresponding foo.cpp, this takes any headers included by foo.hpp
  as being also guaranteed for foo.cpp.

- Use C-style <foo.h> instead of <cfoo>, since the latter only
  guarantees putting symbols in the `std` namespace, which we are
  not using for C functions (e.g. `printf` not `std::printf`).

- Remove now-unused `__PRETTY_FUNCTION__` reporting

src/extern/utf8decoder.cpp

@@ -2,7 +2,7 @@
 
 /* UTF-8 decoder: http://bjoern.hoehrmann.de/utf-8/decoder/dfa/ */
 
-#include <stdint.h>
+#include "extern/utf8decoder.hpp"
 
 static const uint8_t utf8d[] = {
     0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 00..0f */