esp8266: Add Python modules for initial configuration.

Main entry point is _boot.py which checks whether FAT FS in flash mountable,
and if so, mounts it. Otherwise, it checks if flash is empty, and if so,
performs initial module setup: makes FAT FS, configures default AP name,
etc. As a last option, if flash is not empty, and could not be mounted,
it means filesystem corruption, and warning message with instructions is
printed in an infinite loop.

esp8266/scripts/inisetup.py

@@ -0,0 +1,31 @@
+import uos
+import network
+from flashbdev import bdev
+
+def wifi():
+    import ubinascii
+    ap_if = network.WLAN(network.AP_IF)
+    ap_if.config(essid=b"MicroPython %s" % ubinascii.hexlify(ap_if.mac()[-3:]))
+
+def check_bootsec():
+    buf = bytearray(bdev.SEC_SIZE)
+    bdev.readblocks(0, buf)
+    empty = True
+    for b in buf:
+        if b != 0xff:
+            empty = False
+            break
+    if empty:
+        return True
+    fs_corrupted()
+
+def fs_corrupted():
+    import time
+    while 1:
+        print("""\
+FAT filesystem appears to be corrupted. If you had important data there, you
+may want to make a flash snapshot to try to recover it. Otherwise, perform
+factory reprogramming of MicroPython firmware (completely erase flash, followed
+by firmware programming).
+""")
+        time.sleep(3)