[feature] v2 (improved notation)

[pgarciacamou]

Fixes #7

Checklist

• [x] I have made a material change to the repo (functionality, testing, spelling, grammar)
• [x] I have read the [Contribution Guide] and my PR follows them.
• [x] I updated my branch with the master branch.
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have added necessary documentation about the functionality in the appropriate .md file
• [x] I have added inline documentation to the code I modified

Short description of what this PR does:

• Introduces array notation with mapContextToProps
• Deprecated context wrapper explained in #7. Renamed to UNSAFE_withContext.
• Previous comma-separated context API list was named as withContextAsProps and injects the context as separate props into the component.
• Individual exports to allow tree shaking capabilities.
• Adds a list of contributors.
• Updates specs and adds more to the new features.

Code example

If [A,B,C] are Context APIs and [a,b,c] are the consumed context, then:

Before:

• withContext(A,B,C)(Comp) -> <Comp context={...a, ...b, ...c} />

Now:

• withContextAsProps(A,B,C)(Comp) -> <Comp {...a} {...b} {...c} />
• withContext([A], mapContextToProps)(Comp) -> <Comp {...mapContextToProps({...a}) />

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This PR also included validations. I opted to remove that feature because the use of invariant, react-is, lodash.isfunction, and lodash.isstring were bloating the size of the library from 2KB to 20KB.