Std.getenv(key, default_value) variant

[ynohtna]

A simple 2 argument variant of Std.getenv where the second string argument is the default value returned if the requested environment variable is unset.

Simplifies

Std.getenv("COOL_PROG_OSC_ADDRESS") => string addr;
if (addr == "") {
  "127.0.0.1" => addr;
}

to Std.getenv("COOL_PROG_OSC_ADDRESS", "127.0.0.1") => string osc_in_port;