1. Mention multiplex as a dependency
2. Add ERB as a MIME-type

Closes #4020

Closes #4012

Closes #4009

Issue #4013

Closes #4013

Closes #3994

Issue #4001

Use it to make the C++ mode not indent template statements

Closes #4001

according to Clojure's changelog: https://github.com/clojure/clojure/blob/master/changes.md

Closes #3981

Issue #3973

@ as __matmul__ operator only on Python 3,

Add tests for Python mode for this use case.

Closes #3957

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

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 #3932

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

Closes #3922

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.

Issue #3911