Issue #3974

Even if we don't use promise internally, check for the existence of
`.then` attributes on the return results of a hinting function, and if
so assume it is a promise.

Internally also convert all hinters to use the asynchronous interface
for consistency and simplification of code paths.

Closes #3971

`u` prefix are valid (again) since 3.3, and `f` prefix are now allowed
starting at 3.6 (which is not released yet though).

Closes #3972

Issue #3956

There were two issues:

1. Github flavored markdown calls Objective C `objective-c`
2. The gfm.js mode didn't include `-` in its fenced code block regex

Additionally, test/index.html did not import the mode/meta.js file,
which prevented mode lookup by name from working in unit tests.

Issue #3941

Issue #3932

BUCK, BUILD, *.BUILD and *.bzl files are build files for the three build
systems mentioned, and they are all valid Python files.

5.13.4 was a trivial release restoring a LICENSE file.

Issue #3938

Closes #3934

Closes #3922

Closes #3920

Closes #3914

The 6 "n"s are reported as suspicious code by Closure Compiler.
They can just be empty statements instead.

This eliminates a warning from Closure Compiler.

The Error after the while(true) loop is not reachable and should
be removed. The "this.iterator" property should be given an
initial value of 0. This fixes two warnings reported by Closure
Compiler.

Issue #3911

Added tests and fixed some issues uncovered by testing.