Add API for accessing command-line arguments.

- Add process module with Process class.
- Add "arguments" and "allArguments" methods.
- Docs for same.
- Support passing additional arguments to command line.
- Add "--help" support to command line.

test/process/all_arguments.wren

@@ -0,0 +1,11 @@
+import "process" for Process
+
+var args = Process.allArguments
+System.print(args is List) // expect: true
+System.print(args.count)   // expect: 2
+
+// Includes wren executable and file being run.
+System.print(args[0].endsWith("wrend")) // expect: true
+System.print(args[1]) // expect: test/process/all_arguments.wren
+
+// TODO: Test passing additional args once we have an API to spawn a process.

test/process/arguments.wren

@@ -0,0 +1,6 @@
+import "process" for Process
+
+// No additional arguments are passed to the test.
+System.print(Process.arguments) // expect: []
+
+// TODO: Test passing additional args once we have an API to spawn a process.