Use entry_points instead of scripts

[iamdefinitelyahuman]

Simple Summary

Vyper's compiler scripts should be installed via entry_points and made available as vyper.cli

Abstract

Using entry_points instead of scripts removes the need for if __name__ == "main": within Vyper's command-line scripts. Placing the functionality within a main() method simplifies writing unit tests. Migrating the scripts to vyper/cli allows them to be imported and accessed by other packages.

entry_points also provides better cross-platform compatibility, and it's use is recommended over scripts within the PyPA docs.

Motivation

• I need to write unit tests for add root path, search for imports in multiple folders #1570
• 3rd party tooling written in python should be able to access the full range of the compiler's functionality without relying on a subprocess call to reach bin/vyper

Specification

• modify setup.py
• replace if __name__ == "main": with def main(): in all bin scripts
• move the bin folder to vyper/cli, add .py suffix to files

Backwards Compatibility

Should not cause any issues as scripts will still be invoked via the same commands, and the bin folder was not previously available to import as a package.

Copyright

Copyright and related rights waived via CC0

[jacqueswww]

Yeah this doesn't really even need a VIP IMHO. #1337 also implements this if I recall correctly.
#1128 will be fixed with using entrypoints.

[jacqueswww]

Removed VIP, and yes - just do it :)