add support for file format ELF (Executable and Linkable Format)

[atsju]

Hello,
I'm using this tool for years now, especially to add CRCs to hex files.

I work in embedded and arm-none-eabi-gcc which is one of the main compilers generated .elf files (also named .axf or .out depending on the MCU manufacturer). I think the format is this one : https://en.wikipedia.org/wiki/Executable_and_Linkable_Format

It's more or less industry standard. Could you please add support to this format in srecord ? As of today, I'm using objcopy to work only on Intel Hex files but it's not ideal.
Maybe it's beyond the scope of srec_cat.