docs: Rename esp_pthread docs to pthread, expand details of supported APIs

- Move the code that was in the document out to an example

examples/system/pthread/example_test.py

@@ -0,0 +1,27 @@
+#!/usr/bin/env python
+
+from __future__ import division, print_function, unicode_literals
+
+import re
+from typing import Any
+
+import ttfw_idf
+
+
+@ttfw_idf.idf_example_test(env_tag='Example_GENERIC', target=['esp32', 'esp32s2', 'esp32c3'])
+def test_examples_pthread(env, _):  # type: (Any, Any) -> None
+    app_name = 'pthread'
+    dut = env.get_dut(app_name, 'examples/system/pthread')
+    dut.start_app()
+
+    # Note: this test doesn't really confirm anything, except that threads are created
+    # and stdout is not being corrupted by multiple threads printing ot it.
+    dut.expect(re.compile(r'Created thread 0x[\da-f]+'))
+    dut.expect(re.compile(r'Created larger stack thread 0x[\da-f]+'))
+    dut.expect(r'Threads have exited')
+    dut.expect(re.compile(r'Created thread 0x[\da-f]+ with new default config'))
+    dut.expect('Thread has exited')
+
+
+if __name__ == '__main__':
+    test_examples_pthread()