Set fifo rate and mpu addr

[whyameye]

2 small changes to dmpInitialize():

• before this change dmpInitialize() would set the FIFO rate at 100hz (hardcoded). This commit adds an optional parameter to set the FIFO rate and defaults to 100hz if no parameter is given. Rate is calculated by (200/(1+x)) where x is the optional parameter and defaults to 1.
• before this change dmpInitialize() assumes the MPU6050 address is 0x68 (hardcoded). This commit adds an optional parameter to set the address and defaults to address 0x68 if no address is given.

slowing down the FIFO rate was my workaround to address issue #16. Theis commit maintains backward compatibility.

[sabas1080]

@whyameye thank you for your contribution, please check the unit tests or the github action, it seems that the structure of the functions has not been completely changed.

[whyameye]

the only failures I'm seeing are all related to the example I pushed in the last PR and that's because that code is specifically written for the LGT8F328p. What am I not seeing specifically?

[whyameye]

oops sorry I see the errors now. I'll look into it.

[xpeqex]

@whyameye

No worries, we will be waiting for the changes.

[whyameye]

I was too hasty. Still not right even though checks passed. Don't merge yet.

[whyameye]

OK I think this PR is good now. Let me know if you see any other problems.

[DeimosHall]

LGMT