added macro for max open SPIFFS files, setting it to 1 saves about 1k heap

[tijnkooijmans]

Since heap is so precious on this chip, I though this might be of use. Most applications I write don't need more then 1 file open simultaneously.

[codecov-io]

Current coverage is 27.61%

Merging #2167 into master will not change coverage

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[kaeferfreund]

like this one 👍

[reaper7]

I can define that value inside sketch?
#define SPIFFS_MAX_OPEN_FILES 2

[igrr]

@reaper7 you can, but it will not have any effect.
This needs to be defined when compiling core cpp files.
I suspect @tijnkooijmans is not using Arduino IDE to build the code, so he can add this define to compiler flags.

[tijnkooijmans]

indeed, I use platformIO in which you can set build flags in platform.ini

[reaper7]

@igrr & @tijnkooijmans - thx for clarification