ports: Make new ports/ sub-directory and move all ports there.

This is to keep the top-level directory clean, to make it clear what is
core and what is a port, and to allow the repository to grow with new ports
in a sustainable way.

ports/esp8266/modules/_boot.py

@@ -0,0 +1,13 @@
+import gc
+gc.threshold((gc.mem_free() + gc.mem_alloc()) // 4)
+import uos
+from flashbdev import bdev
+
+try:
+    if bdev:
+        uos.mount(bdev, '/')
+except OSError:
+    import inisetup
+    inisetup.setup()
+
+gc.collect()