Add a Platform class.

- Rename the "process" module to "os".
- Add Platform to it.
- Static "name" method.
- Static "isPosix" method.
- Docs and tests!

test/os/platform/is_posix.wren

@@ -0,0 +1,5 @@
+import "os" for Platform
+
+// Can't test for certain values since this test is cross-platform, but we can
+// at least make sure it is callable and returns a bool.
+System.print(Platform.isPosix is Bool) // expect: true

test/os/platform/name.wren

@@ -0,0 +1,5 @@
+import "os" for Platform
+
+// Can't test for certain values since this test is cross-platform, but we can
+// at least make sure it is callable and returns a string.
+System.print(Platform.name is String) // expect: true

test/os/process/all_arguments.wren

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+import "os" 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/os/process/all_arguments.wren
+
+// TODO: Test passing additional args once we have an API to spawn a process.

test/os/process/arguments.wren

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+import "os" 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.