feat: add buildmanual target, faker demo, subprocess examples, and contributing sidebar to manual

Add Makefile buildmanual target for manual generation and include faker_demo.wren, subprocess_async_demo.wren, subprocess_concurrent_demo.wren, and subprocess_fiber_demo.wren example scripts. Update manual sidebar across api pages to link new web-server tutorial and contributing section with module architecture, pure-wren/c-backed modules, foreign classes, async patterns, testing, and documentation pages.

test/subprocess/popen.wren

@@ -0,0 +1,16 @@
+// retoor <retoor@molodetz.nl>
+
+import "subprocess" for Popen
+
+var p1 = Popen.new(["echo", "test"])
+System.print(p1.pid > 0) // expect: true
+var out1 = p1.stdout.read()
+System.print(out1.trim()) // expect: test
+System.print(p1.wait()) // expect: 0
+
+var p2 = Popen.new(["cat"])
+p2.stdin.write("hello")
+p2.stdin.close()
+var out2 = p2.stdout.read()
+System.print(out2) // expect: hello
+System.print(p2.wait()) // expect: 0

test/subprocess/popen_basic.wren

@@ -0,0 +1,9 @@
+// retoor <retoor@molodetz.nl>
+
+import "subprocess" for Popen
+
+var p = Popen.new(["echo", "hello"])
+var output = p.stdout.read()
+System.print(output.trim()) // expect: hello
+var code = p.wait()
+System.print(code) // expect: 0

test/subprocess/popen_pty.wren

@@ -0,0 +1,11 @@
+// retoor <retoor@molodetz.nl>
+
+import "subprocess" for Popen
+
+var p = Popen.new(["sh"], true)
+System.print(p.pid > 0) // expect: true
+p.stdin.write("echo pty_test\n")
+p.stdin.write("exit\n")
+var out = p.stdout.read()
+System.print(out.contains("pty_test")) // expect: true
+System.print(p.wait()) // expect: 0