rename the output binary, identify the binary from cli version

[InoMurko]

Description

This is part of the investigative work for supporting installable solc (or is it osolc?) #24.

In order to support developers developing for both Ethereum L1 and Optimism L2, solc compilers should be able to live side by side, unrelated to each other. So this PR renames the output binary from solc to osolc and adds a small change to the cli --version string.

Based on this work I would continue:

• start publishing releases and packages of the repository, similar to https://github.com/ethereum/solidity/releases. This is essential so that we start attaching assets that we can reference in package managers (like asdf and brew below) and so that we have change logs published. This is a hard requirement for installable solc from popular package managers #24.
  Oh well... the problem at this step is that I don't have the permissions! :-)
• with the changes to other supported versions of the compiler, 0.6, 0.7, 0.8
• solcjs should also be renamed, possibly with the same o prefix
• fork https://github.com/ethereum/homebrew-ethereum into ethereum-optimism and adapt to osolc
• fork https://github.com/refillic/asdf-solidity into ethereum-optimism and adapt to osolc

Checklist

• Code compiles correctly
• All tests are passing
• New tests have been created which fail without the change (if possible)
• README / documentation was extended, if necessary
• Changelog entry (if change is visible to the user)
• Used meaningful commit messages