Squashed commit of the following:

commit 89e9d426e91c056e659fccf5e5c4392618f8f777
Author: Gregory Nutt <gnutt@nuttx.org>
Date:   Mon Jul 24 16:44:19 2017 -0600

    Update some comments

commit 9c5d8a5833350006ed389e898b11c8c8a20e5f4f
Author: Gregory Nutt <gnutt@nuttx.org>
Date:   Mon Jul 24 16:15:54 2017 -0600

    Spirit:  Rename drivers/wireless/spirit/src to lib.  Move Spirit network driver out of IEEE802.15.4 into drivers/wireless/spirit/drivers

commit cabc0ec9e6eb558dcb715ab17264383aa0105e7a
Merge: 87b616414a 6bd744c4
Author: Gregory Nutt <gnutt@nuttx.org>
Date:   Mon Jul 24 15:38:40 2017 -0600

    Merge remote-tracking branch 'origin/master' into spirit

commit 87b616414a79c01a71acea78f8258e05325c1996
Author: Gregory Nutt <gnutt@nuttx.org>
Date:   Mon Jul 24 15:37:27 2017 -0600

    Spirit radio driver is mutating into a standalone network driver.

commit 507798233868a661ae8adad3e3aa117075a7a146
Author: Gregory Nutt <gnutt@nuttx.org>
Date:   Mon Jul 24 13:32:08 2017 -0600

    Spirit: More radi...