Rename SLCD geometry tructure to attributes;  Move MAX contrast to attributes.  Add  attribute and ioctl commands to get and set SLCD brightness

Converted all configurations to use the kconfig-frontends tools, cleaned up the directory structure and naming to match some of the more recent configurations, and added a segment LCD driver for the board.  The initial checkin of the LCD driver is just a clone of configs/pcblogic-pic32mx/src/pic32mx_lcd1602 and it not yet expected to be functional.

PCB-Logic PIC32MX LCD1602 driver now supports SLCD CODED; Added an SLCD ioctl command to get cursor position

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.

Add apps/examples/slcd, Remove USB from STM32L-Discovery, LSE support for the STM32 L family, some STM32L-Discovery LCD debug changes

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

Add audio/ sub-syste, include/nuttx/audio.h interface, and drivers/audio/vs1053.c driver to NuttX.  From Ken Pettit

Add kernel build support and a kernel most OS test example for the Mikroe STM32 M4 board.  From Ken Pettit

apps/examples/helloxx entry point name was mangled when built as an NSH builtin; plus some README updates