Make uBitcoin a dependency

[ThomasFarstrike]

This works fine for me, using the Arduino IDE (1.8.13) on Linux.

I don't see any conflict, but I did notice that esp-idf 5.3.2 has these 2 files called hash.h:

./esp-idf_5.3.2/components/mbedtls/mbedtls/tests/include/test/drivers/hash.h
./esp-idf_5.3.2/components/openthread/openthread/third_party/mbedtls/repo/tests/include/test/drivers/hash.h

They're lowercase hash.h, so (at least on Linux and MacOS) that's different from the Hash.h in uBitcoin.

I doubt these would conflict, even on Windows, but if you have any issues, please me know and then we can look for another solution :-)

Thank you!

[riccardobl]

Just to be clear, the issues i was referring to were related to ports to non esp platforms.
I believe picow, but i had other issues in porting the library there that makes it basically unsupported atm.
So i will merge this PR for now, since it makes things easier for esp32.

Thank you.

[ThomasFarstrike]

Sweet!