Massive set of fixes and improvements.

Thanks to contributors: @cheerypick, @swan46, @MacKLess, @Elrendio, @madman-bob, @Amanda-bot, @Hirse, @aeschli, and many more.

Special thanks to @astronomersiva and @garretwilson for finding key bugs in the RC releases,
and to @MacKLess for driving down the open bug count with tons of regression tests.

Highlights:

• CSS: newline_between_rules support for nested rules - CSS/SASS/SCSS/LESS (@MacKLess)
• CSS: @import support in CSS (@MacKLess)
• HTML: inline element support (@madman-bob)
• HTML: wrap_attributes setting align-multiple (@cheerypick)
• HTML: optional close tags do not over indent - li, tr, etc.
• HTML: Improved line wrapping in HTML - still not fully correct
• HTML: 10x performance improvement in HTML beautifier
• JS: ES6 BigInt support (@thejoshwolfe)
• JS: ES6 Dynamic import support
• CSS: :hover for @extend formatting (@MacKLess)
• HTML: Incorrect line wrapping issue (@andreyvolokitin)
• JS: Javascript ++ Operator Indentation (@Elrendio)
• JS: Better packer handling in Python (@swan46)