HTTP server, scripting, and performance

This is the third preview release of Ink. The language specification has stayed unchanged, and the interpreter comes with these improvements.

• The listen(host, handler) builtin function for starting HTTP servers written in Ink
• Optimizations to composite value accesses and number-to-string conversions
• A more stable parser, especially when parsing partial input in the -repl
• Optimized functions in the standard library, specifically work to make std.encode faster and bug fixes to std.readFile and std.writeFile
• Support for using the ink interpreter in an Ink script's #!/usr/bin/env ink shebang line
• General other minor bug fixes and optimizations

You can once again go to https://linus.zone/eval to try the newest version of the interpreter, minus file read/write operations and the new listen(...) builtin -- those are limited by the -isolate interpreter flag.