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

Added tests and fixed some issues uncovered by testing.

corrected angle bracket matching in operators (fixes block comments)
corrected digit matching regex
corrected spelling of 'identifier' in grammar dictionary
notCharacterOrDash explicitly includes lowercase characters
improved variable matching
splatted variables now match
bare '$' and '@' are errors, not variables
moved single-quoted string processing into tokenSingleQuoteString
incomplete strings are errors now
empty strings are no longer errors
added support for here-string interpolation with nesting support
added highlighting for splatted vars
removed arbitrary stream advancement prior to default error in tokenBase
enabled folding braces