Automatically choose correct IDE download

[per1234]

Currently install_ide is hardcoded to download the Linux 64 bit versions of the Arduino IDE.

• Windows: [[ "$OSTYPE" == "cygwin" ]] || [[ "$OSTYPE" == "msys" ]] (https://stackoverflow.com/a/8597411)
• macOS: [[ "$OSTYPE" == "darwin"* ]] (https://stackoverflow.com/a/8597411)
  • There are some 1.5.x tags that appear to be macOS specific so that might need special handling:
    • 1.5.7-macosx-java7
    • 1.5.8-macosx-java7
• Linux 32-bit: ?
• Linux 64-bit: ?
• ARM Linux: ?