feat: add support for Rollup 60

[tivac]

This takes advantage of the new plugins APIs introduced in rollup/rollup#2208

modular-css-rollup will now support automatic chunks via multiple inputs and manual chunking of vendor files via manualChunks. It might also support dynamic import but I haven't written tests for that yet.

This is a ⚠️ BREAKING CHANGE ⚠️, it will only be compatible with rollup@0.60 and higher.

[codecov]

Codecov Report

Merging #429 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master    #429   +/-   ##
======================================
  Coverage    99.1%   99.1%           
======================================
  Files          35      36    +1     
  Lines         779     779           
  Branches      114     113    -1     
======================================
  Hits          772     772           
  Misses          7       7

Impacted Files	Coverage Δ
packages/test-utils/exists.js	100% <100%> (ø)
packages/rollup/rollup.js	100% <100%> (ø)	⬆️

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