Add instructions to enable RTC in the nsh/ configuration; RTC enabled by default in the demo configuration

SAMA5 LCD:  Move framebuffers to center of free memory region.  That creates a guard band around the framebuffers that gives a little protection from any bad writes into the framebuffer

Enhanced the FAT32 filesystem code to understand DMA preflight failures, and to use the file sector buffer as a bounce buffer when a user-supplied buffer is not suitable for DMA. From Mike Smith

Enhanced the mmcdd_sdio driver to perform DMA preflight operations and fail DMA read/write requests that fail preflighting. From Mike Smith

Minor tweaks to debug output; started renaming some icons to include size in the name; SAMA5 NxWM config needs libm

New touchscreen scaling algorithm for the case where measured X values vary with y position (and vice versa)

net_sendfile:  Let the ACK callback handle the REXMIT flag and don't return until all data has been ACK'd. From Max Holtzberg

Move tcp connection into SYN_RCVD state after aception instead of bypassing and moving directly into ESTABLISHED.  From Max Holtzberg.

NxWidgets::CScaledImage: New class that wraps any class that provides IBitMap and adds image scaling

NxWM::CCalibration: Add logic to collect and average samples, optionally discarding the most extreem values

Misc changes to README files; Update SAMA5D3x-EK NxWM configuration to use Calibration instruction messages