[Feature Request] Allow different CAN bit rates

[fastbike]

Currently the CAN module only support bit rates of 125k, 250k, 500k and 1M bits per second.

Other libraries support the setting of bit rates in a more flexible way allowing an integer to be passed in.

I'm currently looking to build a project to work with Velbus which uses a bit rate of 16.7kbps.

There are many other products in the marketplace using a bit rate different to the 4 listed above.
I would looking for something like

bool R7FA4M1_CAN::begin2(int const can_bitrate)

[fastbike]

I have created a fix by overloading the R7FA4M1_CAN::begin function to accept either the predefined bit rates or an integer value

  bool begin(CanBitRate const can_bitrate) override; // enum values
  bool begin(uint32_t const can_bitrate); // integer values

This has been tested with the four enum values, and also with 83300, 50000, 40000 and 16666 baud

Baud	BRP	TSEG1	TSEG2
1M	1	7	2
500,000	2	10	3
250,000	5	10	3
125,000	11	10	3
83,300	15	11	4
50,000	23	13	4
40,000	29	13	4
16,666	71	13	4