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/platform.markdown

@@ -0,0 +1,26 @@
+^title Platform Class
+
+The Platform class exposes basic information about the operating system Wren is
+running on top of.
+
+## Static Methods
+
+### **name**
+
+The name of the platform. This roughly describes the operating system, and is
+usually one of:
+
+* "iOS"
+* "Linux"
+* "OS X"
+* "POSIX"
+* "Unix"
+* "Windows"
+
+If Wren was compiled for an unknown operating system, returns "Unknown".
+
+### **isPosix**
+
+Returns `true` if the host operating system is known to support the POSIX
+standard. This is true for Linux and other Unices, as well as the various Apple
+operating systems.