Convert to wrapper for ccurl library

[todofixthis]

Convert the extension into a wrapper for the official CCurl library.

This gets us a ton of goodies for free:

• Crypto code is already/regularly vetted.
• Any enhancements or fixes made to the CCurl library would automatically apply to us.
• We'd be able to seamlessly incorporate PoW.

[furuame]

Why don't just use ctypes to load the existing ccurl library to do PoW?

[todofixthis]

That could work, too. Maybe better — as long as we can do a one-command install (i.e., pip install pyota[ccurl]), then I'm not too precious about how it works under the hood (:

[furuame]

Is one-command install necessary? ccurl.interface.js also needs extra steps to build ccurl.
I'm not familiar with Python, but I am curious if there is a way to do these steps automatically.

If that's the case, pyota-ccurl only need implement an interface to load PoW library, which is like ccurl.interface.js.