Postcss Import Versions Save

This release should not have breaking changes for the vast majority of users; only those with @charset statements in their CSS may be affected.

• BREAKING: Error if multiple incompatible @charset statements (#447)
• BREAKING: Warn if @charset statements are not at the top of files (#447)
• Fix handing of @charset (#436, #447)

• BREAKING: Require Node 10+ (#429)
• BREAKING: Upgrade to postcss v8 and require it as a peerDependency (#427, #432)
• Update dependencies

• Removed: Support for Node.js v4
• Changed: Uses PostCSS v7 (https://github.com/postcss/postcss/releases/tag/7.0.0)

• Added: filter option

• Changed: A syntax error in an imported file now throws an error instead of just warning (#264)
• Changed: Symlink handling to be consistent with Node.js require (#300)

• Removed: Support for Node.js versions less than 4.5.x (#283)
• Changed: Upgraded to Postcss v6 (#283)
• Removed: jspm support (#283)
• Removed: deprecated addDependencyTo option
• Removed: onImport option
• Changed: Doesn't depend on promise-each (#281)

• Added: addModulesDirectories option (#256)

• Removed: transform option (#250)
• Removed: pkg-resolve is no longer a dependency; this should fix some issues with webpack. jspm users must manually install pkg-resolve if they want to load jspm modules (see https://github.com/postcss/postcss-import#jspm-usage for more info) (#243)
• Changed: If a file is not found, it will now throw an error instead of just raising a warning (#247)
• Changed: If a custom resolver does not return an absolute path, the default resolver will be applied to the returned path. (#249)
• Changed: postcss-import will try to guess the correct parser for imported files, based on the file extension. (#245)
• Changed: Deprecated addDependencyTo option, it is not needed if using postcss-loader >= v1.0.0 (#251)

• Fixed: Warn about all @imports after other CSS declarations (#240)
• Added: dependency message (#241)

• Fixed: Nested import ordering (#236 - @RyanZim)