Ink 1.7: runtime builtins overhaul

Language core

There are no significant changes to language syntax or semantics in this update.

Language builtin interfaces

• 407fabb Guard against sending invalid HTTP status codes through listen()
• 98b5f7e Update delete() to delete filesystem nodes recursively
• 87a1705 Add "mod" to stat() return value
• 315e7c6 Add "mod" to return value of dir()
• 828dfd1 Add args() builtin for getting argv[]
• 861c9df Add urand() for cryptographically safe RNG
• 822c2ed Update exec() to send event objects, not just output string
• 6f18152 Update make() to use MkdirAll, not Mkdir (make directories recursively)
• 8ec1912 Add asin() and acos() to runtime

Standard Library

• ba75c51: std.writeFile now truncates files before writing them, so writeFile-ing a shorter file will work as expected.
• 59d0a79 optimization: std.slice now mutates one string instead of creating many, O(n) memory allocation instead of O(n^2)