AirSpy Firmware version v1.0.0-rc4

Modifications for rc4:

• Add support of get_samplerates command
  (see latest host tools+dll: https://github.com/airspy/host/releases)
• MD5 for https://github.com/airspy/firmware/releases/tag/v1.0.0-rc4 (build on 2015-03-22):
  md5sum airspy_fw/airspy_rom_to_ram/airspy_rom_to_ram.bin
227235c5fb868d6a464e47037fb75535 airspy_fw/airspy_rom_to_ram/airspy_rom_to_ram.bin
airspy_fw/airspy_rom_to_ram/airspy_rom_to_ram.bin Size 17 920 bytes

Note:
- This firmware support only 10MSPS & 2.5MSPS.
- Becareful if you build it yourself the `date` of the day is included in `airspy_rom_to_ram.bin`, 
so if you want to have same MD5 you need to change your PC date to 2015-03-22 just before to build it.

• To flash the latest firmware in attachment airspy_fw_v1.0.0-rc4.zip
• For Windows:
  • 1. Extract the archive
  • 2. Connect AirSpy with USB to your computer
  • 3. Launch airspy_spiflash.bat from extracted archive directory
  • 4. Disconnect AirSpy from USB computer
  • 5. Connect AirSpy with USB to your computer, now you can use your favorite software