Update links in Readme.md

Link to FRDM-K64F page, add Nucleo-F302R8, LPC800-MAX, DipCortex-M0, DipCortex-M3, BlueBoard-LPC11U24, link to mbed Platforms page at top of "Supported Microcontrollers and Boards" section.
Added multiple toolchain and MCU declarations for options -t and -m respectively. Names must be divided by comma.
Reduced RPC test scope to LPC1768 for now