Improve Test Runner

[b-studios]

This PR addresses #375 and supports the following formats:

Running tests in examples/neg depends on whether there is a check file or not:

1. .check file exists: .effekt program will be compiled and run; output is compared against .check
2. .check file does not exist: .effekt program will be compiled. The following checks will be performed

• if no line has an error annotation, then it is checked whether an error exists at all.
• for each line that ends in either // ERROR or // WARN a corresponding error or warning is searched for.

Additionally each // ERROR and // WARN comment can be followed by an excerpt of the error message that is expected.

effekt/examples/neg/blocks_wrong_arguments.effekt

Lines 1 to 18 in a103be8

	module blocks_wrong_arguments
	def foo { f : Int => Int } =
	f(2)
	def bar { f : (Int, Boolean) => Unit } =
	f(2, true, 4) // ERROR Wrong number of value arguments
	def main() = {
	val r = foo { (x: Int, y: Boolean) =>
	x + 1
	};
	println(r);
	bar { (x: Int) =>
	()
	}
	}

The trailing message will be searched verbatim in the error messages.

Additional errors that are not marked with a comment are currently ignored.

[b-studios]

@dvdvgt This might be helpful for you to test typer more easily.

[b-studios]

@jiribenes You mentioned the LLVM test runner. Is there anything you think would be super helpful in addition to what I implemented?

[b-studios]

Once the tests go through I will merge this since I already want to use it on another PR :)