Add support for emotion 10

[abalmos]

This adds support for emotion 10. I would love to see this out quickly and would be happy to make edits. The new features are:

Enable template literal and non css prop object styles

Changes:

1. Add @emotion/core and @emotion/styled to supports object. These are the new imports for emotion 10. From postcss-jsx's perspective everything else is the same.

Enable object style for css prop

This is not straight forward anymore. Due to emotion 10's "magic" surrounding React.createElement, the component's namespace does not obviously reference emotion. Template literals in the css prop works because the literal itself can be traced back emotion. Object styles can not. The strategy used here (for lack of a better idea) is to assume all css props are styles when @emotion/core is imported. This seems reasonable because @emotion/core also treats css props this way.

Changes:

1. Add cssPropsImpliesStyle object and cssPropsIsStyle flag. I wrote this to be generic like the supports object in anticipation others will follow emotion 10's lead.

This fixes #43

[codecov]

Codecov Report

Merging #44 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #44   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          20     20           
  Lines         486    490    +4     
=====================================
+ Hits          486    490    +4

Impacted Files	Coverage Δ
extract.js	100% <100%> (ø)	⬆️

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[ianvieira]

Was this change reverted? I some changes were removed at #45

[gucong3000]

Was this change reverted?

Updated, but test cases are preserved here: https://github.com/gucong3000/postcss-jsx/blob/master/test/fixtures/emotion-10.jsx