Release candidate N2.3

Release candidate N2.3:

• Move core-js from dev to runtime dependencies (closes #28, #29)

Release candidate N2.2

• Support new process assets in webpack 5 #24 (posted by @dotnetshadow)
• Fix types for Webpack Plugin #18 (fixed by Mikhail Bodrov)

Release candidate N2.1

• Update for CSSO 4
• Drop maintenance for NODE < 8.0.0 (see csso v4 release notes, it's incompatible)

Resolved: #15, #16, #22.

Chores:

• use native async/await instead async
• moved to source-map with support WEBAssembly
• Up-to-date dev-dependencies versions

Release candidate N9

• Fix warning with webpack 4.x (thanks for @the-spyke):

DeprecationWarning: Tapable.plugin is deprecated. Use new API on `.hooks` instead

Release candidate N8

• No changes

Release candidate N8

• Add new option for two different files — pluginOutputPostfix
• csso 3.3.0 -> 3.4.0 by default
• Update-to-date dev-dependencies versions

Release candidate N7

• csso -> 3.3.0 and source-map -> 6.0.1 by default
• Update-to-date dev-dependencies versions

Release candidate N6

• Update-to-date dependencies versions
• BREAKING: options.sourceMap is deprecate and should be removed from config.
  For getting source map just use any value devtool.

Release candidate N5

• Update-to-date dependencies versions
• Trivial; strict 0.10 node version

Release candidate N4

• trivial. Provide typings for Flow and Typescript