Add URL to rule documentation to the metadata

[Arcanemagus]

ESLint v4.15.0 added an official location for rules to store a URL to their documentation in the rule metadata in eslint/eslint#9788. This adds the URL to all the existing rules so anything consuming them can
know where their documentation is without having to resort to external packages to guess.

[codecov-io]

Codecov Report

Merging #102 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #102   +/-   ##
=======================================
  Coverage   98.52%   98.52%           
=======================================
  Files          42       42           
  Lines        1014     1014           
=======================================
  Hits          999      999           
  Misses         15       15

Impacted Files	Coverage Δ
lib/rules/no-extraneous-import.js	90.9% <ø> (ø)	⬆️
lib/rules/no-extraneous-require.js	90.9% <ø> (ø)	⬆️
lib/rules/no-unpublished-require.js	100% <ø> (ø)	⬆️
lib/rules/no-deprecated-api.js	100% <ø> (ø)	⬆️
lib/rules/exports-style.js	98.27% <ø> (ø)	⬆️
lib/rules/no-unsupported-features.js	98.96% <ø> (ø)	⬆️
lib/rules/no-missing-require.js	100% <ø> (ø)	⬆️
lib/rules/no-unpublished-import.js	100% <ø> (ø)	⬆️
lib/rules/process-exit-as-throw.js	95% <ø> (ø)	⬆️
lib/rules/no-unpublished-bin.js	92.59% <ø> (ø)	⬆️
... and 2 more

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[mysticatea]

LGTM, thank you!