Use lzstring R package for encode/decode Shinylive URL functions

[parmsam]

Based on great work from @gadenbuie shared in #70 that used original JS implementation via V8. This PR switches over to lzstring package, updates url_encode_dir(), and adds url_decode() based on the Python implementation here and here. Nearly there, just seems to add an empty line at the end of scripts on the URL decode. Not complete but aims to get work started again.

Example to try out:
shinylive:::url_decode(encoded_url = "https://shinylive.io/r/editor/#code=NobwRAdghgtgpmAXAAjFADugdAJTAGlQGMB7CAFzgqVQBsBLAIwCcpmBPACgGcALeiOwCUAHQhiAxMgAicAGYC4yAKoBJZHJLNkGdMnK8o5ZABNWAd247k-buRIBzVjGQBad67EBXesgA8rhq0PiYAClAOcJxiyMgxyFIAgpj69OS0Sh6eELHkaRnhEHC00WAAEsW0JMgAyvyCAIQiYEL48fFSNfQmcIxsyLRQ7CRexuZpvMgC6KM6ECbII+Qzxj0KEGn0ZFZZ8dzdvWwAMkNL0TmxcRexnQd92uhQRbQaWlMQKzse8bH7PfeFYrnS6XH6XKSqD6jFA1Bg9bSabQGJQQLwwRhwbQkOTIRgCL7uMG-OGYyErTjTUaqBYAXjiYDxEG4zTa1xB7I5gwxLzpzQAcmiMVicYzuIgWUSOVKYAJkHSAIysqXKy4wKAADzlyAArAAGJUq5UANygwSUdIAzLrRGzYmDWmCwVIALJQWWPZ6vbQmejcdCDdgCByLUafNzfNlqgSAkqSyVSADyoehyDKvvsTlg4cJtuQ-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-FRAISVVTdHJeXKdNaJcB9as2H68ngZkWkdC4AF95rEAmxHbABhJTRLqAR2B0FJdiZep2GSdBOB8LUfEIVd1y1HnMRtAhUFi+KaDASggbAAmAF0gA", dir = "shinylive_test_code")

shinylive:::url_encode_dir("shinylive_test_code")

[parmsam]

@wch - Following up on this based on our in-person conversation today. Thanks!