Implement automatic selector if plugins are used

[kaste]

Fixes #16

The strategy here is to use a wide selector in the beginning and
then narrow it down during actual linting.

SublimeLinter needs a good selector as a fast check to match
views and installed linters because this first check runs on a shared
worker. T.i. we cannot just select all views and then decide later.

After the first check, it is always possible to abort loud or silently.
We do here silently because it's not a configuration error coming
from the user but an automatic algorithm bailing out.

With this implementation there comes the drawback that we have to flip
the previous default behavior. The default behavior was for the linter
to run on parts of the buffer marked as source.js concurrently. E.g.
it did run on the <script> tags when viewing a HTML file.

However, this default often did not produce good results. I.e. in an
HTML file it has no notion of gloabls introduced in one script which
are accessible in another script.

If the user wants this behavior, she now has to opt in by setting the
old selector 'source.js - meta.attribute-with-value' in the settings
on her own.

Implementation risks:

• We deep import read_json_file. It is possible that this import can
  break since deep imports are not protected by any deprecation policy.

• We have two side-effects: self.notify_unassign() followed by
  raise PermanentError(). It is possible that in the future we need
  to signal the same outcome differently.

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IssueHunt Summary

Referenced issues

This pull request has been submitted to:

• #16: Automatically configure alternative syntax scopes when available

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[kaste]

Er, ping?

[sindresorhus]

Sorry for the slow response. I've just had too many PRs to review.

[sindresorhus]

With this implementation there comes the drawback that we have to flip
the previous default behavior. The default behavior was for the linter
to run on parts of the buffer marked as source.js concurrently. E.g.
it did run on the <script> tags when viewing a HTML file.

I'm fine with that. You should generally have minimal of inline JS, as a best practise.

[sindresorhus]

Can you document the behavior in the readme?

[kaste]

LGTM!

[sindresorhus]

Looks good. Thanks for working on this. 👍