Update documentation on Kernel.var!/2

The documentation is no longer accurate since passing atoms to `Kernel.var!/2` has been deprecated and removed.
Merge pull request #2463 from hamiltop/master

Update documentation on Kernel.var!/2
Release v0.14.2
Start v0.14.3-dev
Match test lines by proximity, closes #2450
Improve <<>> docs
Update (soft) deprecations
Improvements to the operator table

  * |>, <<<, >>> and ^^^ were made left associative

  * <, >, <=, >= were given higher precedence than
    comparison ones (==, !=, etc)

  * xor is deprecated