Expose 'raw' option for css in types

[fpapado]

Hello again! I thought to split this into a separate one, in case there is any iteration needed.

Proposed changes

The code and tests show that it is possible to specify a 'raw' option for css:

    css: [
      {
        raw: style,
        extension: 'css' // Technically not needed; see below
      }
    ],

Existing code segment with functionality:

purgecss/src/index.js

Line 124 in 148e2db

cssContent = option.raw

Test using it:
https://github.com/FullHuman/purgecss/blob/master/__tests__/purgecssDefault.test.js#L323

However, the type interface does not expose it as an option. Thus, if you're using Typescript or Flow and try to use the raw option for css, an error is raised:

  Type '{ content: { raw: string; extension: string; }[]; css: { raw: string; extension: string; }[]; ext...' is not assignable to type 'Options'.
    Types of property 'css' are incompatible.
      Type '{ raw: string; extension: string; }[]' is not assignable to type 'string[]'.
        Type '{ raw: string; extension: string; }' is not assignable to type 'string'.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• [~] New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

NOTE:
I went with RawContent as the option for consistency with the content interface. This type is technically true, but the extension field is not used by the code (since it would be css anyway); this is seen in

purgecss/src/index.js

Line 124 in 148e2db

cssContent = option.raw

I can change it to an explicit type if needed:

type RawCss = {
  raw: string
}

For that matter, I have also not touched the code. Changing the cssOptions: Array<any> in getCssContents would pair well:

getCssContents(cssOptions: Array<string | RawCss>, cssSelectors: Set<string>): Array<ResultPurge> {

// Or

getCssContents(cssOptions: Array<string | RawContent>, cssSelectors: Set<string>): Array<ResultPurge> {

None of these changes would be breaking.

Let me know if any of these alternatives sound better, and I'll get to them :)

[Ffloriel]

Thank you very much for reviewing the types of Purgecss.
I'll review your PRs shortly and merge them.

[Ffloriel]

LGTM