Add an NSH configuration for the Arduino Due; Pluse several fixes related to the Due and to the SAM3X in general

Beginning updates of SAM3U header files o include support for the SAM4S: WDT, SUPC, EEFC, MATRIX, and PMC

Upate .gitignore files.  Add .dSYM. Make sure / is present where needed.  Add some missing .gitignore files

Converted configs/pcblogic-pic32mx configurations to use kconfig-frontends.  Re-organization of files in configs/pcblogic-pic32mx/src

Additional bug fixes and minor extensions to the STM32L-Disovery segment LCD support and to the apps/examples/slcd segment LCD test.

Fix STM32L15X vector definitions; Fix STM32L-Discovery LED controls.  The NSH configuration is now fully functional on the STM32L-Discovery board.

Rearchitecting of some MTD, partition, SMART interfaces, and FLASH drivers to:  Better use the byte write capbility when available and to use smaller erase sectors for the erase sector size when available).

Documentation now expects autogenerated configuration variable documenation at Documentation/NuttXConfigVariables.html