Scalafix v0.5.6

First of all, I am excited to welcome @MasseGuillaume to the Scalafix team! Moreover, I'm also thrilled to see @fommil joining the effort by sponsoring @vovapolu to work on improving scalafix for functional programming, see #451. Consider pitching in too!

Features

• #412 Make it easy to enable sbt-scalafix for custom configurations like
  IntegrationTest with scalafixConfigure(Compile, Test, IntegrationTest), by @olafurpg. See https://scalacenter.github.io/scalafix/docs/users/installation#sbt-scalafix
• #415 Suppress false linter errors with comments, by @MasseGuillaume. This PR makes
  it a lot more practical to use Scalafix for linting, since previously there was no way
  to silence Scalafix for exceptional cases where the linter reports a bogus
  diagnostic. See https://scalacenter.github.io/scalafix/docs/users/configuration#per-source-file
• #426 Upgrade to Scalameta v2.1.2, with support for Scala 2.11.12 and 2.12.4. Scala 2.11.11 and 2.12.3 are still supported, but no older Scala versions.
• #431 New DisableSyntax rule to disable keywords like return/while/throw, by @MasseGuillaume
• #444 Fix off-by-one error in TokenList.next/prev, by @ag91 and @GoldenZero
• #445 skip local implicits in ExplicitResultTypes, by @erikwj
• #448 Add support for attaching custom messages to Disable rule, by @MasseGuillaume. See https://scalacenter.github.io/scalafix/docs/rules/Disable#custom-error-messages
• #448 Add support for asserting against linter messages in testkit, by @MasseGuillaume. Example here.
• #453 use a flexible parser dialect by default that, for example, supports trailing commas, by @olafurpg

Documentation

• #418 Add detailed documentation comparing scalafix with alternative tools
  like Scala Refactoring, WartRemover, ScalaStyle and IntelliJ Scala plugin, by @olafurpg
• #419 Simplify installation of sbt-scalafix with scalafixEnable command that can
  automatically setup all the correct scala compiler settings from an sbt shell session, regardless of
  existing settings in build.sbt. Previously, it was necessary to manually
  update build.sbt with fairly tricky corner cases, by @olafurpg
• #420 New section in the docs for using scalafix with Maven builds, https://scalacenter.github.io/scalafix/docs/users/installation#maven by @fanf

Internal

• #454 refactor the scalafix build for easier cross-building and cross-publishing, by @MasseGuillaume. Please note that there are no published artifacts for v0.5.4 and v0.5.5 due to the build misconfiguration that got fixed by this PR.