Flexible root calls

[BastianBlokland]

Support more kinds of call statements as root statements. The following statements are now legal as root calls:

import "std/console.nov"
import "std/lazy.nov"

print{string}("Hello World")

(print{string})("Hello World")

print("Hello World")

intrinsic{stream_write_string}(intrinsic{console_openstream}(1), "Hello World\n")

act getStream() -> sys_stream
  intrinsic{console_openstream}(2)

act customPrint(sys_stream stream, string message)
  intrinsic{stream_write_string}(stream, message);
  intrinsic{stream_write_char}(stream, '\n');
  intrinsic{stream_flush}(stream)

customPrint(getStream(), "Hello World")

actSeq(
  lazy print("Hello"),
  lazy print("World")
)

Also this PR adds support for calling pure functions in root statements. Even though its not really useful to call a pure
function from the root (as it wont have any output) there is no real reason to disallow it and can be useful for testing.