SPIFFS-related magic constants 0x10000 in Makefile

[mk-pmb]

Expected behavior

1. SPIFFS is flashed to the user-specified location.
2. Files created by the Makefile have meaningful names.

Actual behavior

On branch "dev":

1. I don't know how to verify, but the rules for target flashinternal: look like the pre-created SPIFFS is always written to a fixed location that may differ from user's SPIFFS_FIXED_LOCATION setting. (To increase confusion, the example value in the docs is 0x100000 = 1 MiB ≠ the Makefile value 0x10000 = 64 KiB.)
2. A file bin/0x10000.bin is created, and I have to consult the Makefile to see that it's from a target named spiffs-image:. It should probably better be named sth. like bin/spiffs.img.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[mk-pmb]

I'm still interested.