expose and document createElement and createHelper

[pwmckenna]

Addresses #66.

Happy to update. It is certainly not perfect. There are a couple intentional omissions here:

• introduced ReactChildrenType but didn't really know how to concisely document the type of children...but then again, neither do the react docs ;)
• left out createHelpers's _helperLength, setDisplayName parameters. These don't seem to be used much even internally, and the leading underscore seems to indicate this should remain internal only, so I didn't document the optional params.

[codecov-io]

Current coverage is 100.00%

Merging #116 into master will not affect coverage as of 83ccc93

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  Stmts          325     325       
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  Partial          0       0       
  Missed           0       0       

Review entire Coverage Diff as of 83ccc93

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[acdlite]

I think you're confusing createElement() with toClass(). The purpose of the createElement() is to detect referentially transparent components and call them as functions rather than creating an unnecessary elements. See this doc for more details: https://github.com/acdlite/recompose/blob/master/docs/performance.md

[pwmckenna]

Fair enough, I'll update. I only really care about making createHelper public but it seemed rude to not take a crack at both.

[acdlite]

Haha, not rude at all.

[acdlite]

Let's hold off on this until #117 is resolved. In the meantime, you can import createHelper at recompose/createHelper.