write-bin: Skip writing if binary has not changed.

[Jonathan]

First: I love espflash! It is a great tool! Thanks for all the work!

I'm trying to optimize my flash times by putting static data into a separate partition, which works quite decent via write-bin. But unlike flash, write-bin does not check the MD5 sum of the section and thus does not skip if the same data is already present at that address. This prevents me from adding the write-bin step into the flashing script.

Desired feature:

• Add a --skip-if-present option to write-bin, that checks the md5 hash before writing and skips if it matches the data to be written.

Alternative Approaches:

• allow binary files to be flashed via flash as well
• Default to skipping blocks in general: #588

[Sergio Gasquez Arcos]

• Default to skipping blocks in general: #588

Some initial investigation showed that it was not worth to implement that feature. I would go for adding --skip-if-present flag or the other way, skip by default and add a --no-skip flag like we have in the flash subcommand.