feat: rename process module to os and add Platform class with name and isPosix methods

Rename the "process" module to "os" across all source files, documentation, tests, and build configuration. Add a new Platform class to the os module with static methods `name` (returns OS string like "Windows", "Linux", "OS X", "iOS", "Unix", "POSIX", or "Unknown") and `isPosix` (returns bool indicating POSIX compliance). Update all import paths from "process" to "os" in test files and module registrations. Move process.c/h to os.c/h, rename processSetArguments to osSetArguments, and regenerate the os.wren.inc bytecode source. Add documentation pages for the os module and Platform class.

doc/site/modules/os/process.markdown

@@ -0,0 +1,38 @@
+^title Process Class
+
+The Process class lets you work with operating system processes, including the
+currently running one.
+
+## Static Methods
+
+### **allArguments**
+
+The list of command-line arguments that were passed when the Wren process was
+spawned. This includes the Wren executable itself, the path to the file being
+run (if any), and any other options passed to Wren itself.
+
+If you run:
+
+    :::bash
+    $ wren file.wren arg
+
+This returns:
+
+    :::wren
+    System.print(Process.allArguments) //> ["wren", "file.wren", "arg"]
+
+### **arguments**
+
+The list of command-line arguments that were passed to your program when the
+Wren process was spawned. This does not include arguments handled by Wren
+itself.
+
+If you run:
+
+    :::bash
+    $ wren file.wren arg
+
+This returns:
+
+    :::wren
+    System.print(Process.arguments) //> ["arg"]