Add StrictLocals linter

[wilfison]

StrictLocals

Checks for the presence of a locals magic comment at the beginning of a file. Read more about this in the Ruby on Rails Guides on why it is good practice to define local variables at the beginning of the file.

Bad:

%h1= title

Good

-# locals: (title:)

%h1= title

The new linter follows the same settings as InstanceVariables as designed by @mockdeep in #486

  StrictLocals:
    enabled: true
    file_types: partials
    matchers:
      all: .*
      partials: \A_.*\.haml\z

Close #486

[sds]

Looks great—thank you. Will adjust the default to be disabled so this doesn't come as a surprise to existing users.

[sds]

I would suggest disabling this by default, since it seems like a relatively invasive change for existing codebases.