Bump riscv-rt to v0.11.0

Since Longan Nano GD32VF103 chip only supports
a single hart, still safe to use the recently-
updated riscv crate interrupt free section
which only disables interrupts for the current hart.

Fixes issue where some examples will not build
using memory-c8.x due to flash size constraints

add interrupt example

docs: Add section for serial flashing

Add section to describe flashing firmware over a serial connection

Update LED Shell example

update debugger config

Update dependencies, release v0.3.0

Make converting SD card frequency easier

Use the full screen size to draw the rectangle to clear the screen

Update LCD libraries

Add support for sdcard

Co-authored-by: Vadim Kaushan <admin@disasm.info>

Serial shell example

Add instructions to skip the risc-v toolchain (plus arm64 support)

Add documentation for dfu-util based flashing