Change constructor to take bus and frequency

[nielsvandepas]

Changes the hardware SPI constructor to take 2 optional parameters: the SPI bus to use and the frequency to run it at.

I created this pull request based on the feedback @fabianoriccardi received on #97. This accepts all user-definable parameters for the SPI bus, while staying in control over the parameters which "just have to be this", like the SPI mode. This way it enables the user to change the bus and the frequency without having to read the datasheet or the other code in this library.

[ladyada]

hiya! thanks so much for submitting a PR! we can review & merge PRs once they have passed continuous integration (CI). that means that code compiles cleanly for all tested platforms, is clang formatted so we maintain the same text formatting for all new code, and is doxygen documented. if your code isnt passing, check the CI output (click on the red X next to the PR to scroll through the log and find where the error is

here is a tutorial on doxygen: https://learn.adafruit.com/the-well-automated-arduino-library/doxygen

and clang-format: https://learn.adafruit.com/the-well-automated-arduino-library/formatting-with-clang-format

and overall how to contribute PRs to libraries: https://learn.adafruit.com/contribute-to-arduino-with-git-and-github

once you get that green checkmark that indicates CI has passed, please comment reply to this post so we know its time for another review (we may not get notified on CI pass and miss that its time to look!)

[caternuson]

@nielsvandepas Is setting frequency actually needed? If so, can you provide more information on what platform the current frequency setting is not working with.

The ability to specify an alternate SPI bus was added with #112.

[caternuson]

Closing due to lack of response.