saving some memory space and create a setter for the pin

[pandaroux007]

Hi @mathertel 👋
Thank you for your fantastic work on this library 👍
I have a suggestion to save memory space: use one or more (2, 3...) bytes to store, for example, the pin of the button, like in this library (in French and outside github, sorry 🥴)
➡️ source code
➡️ how it works

Additionally maybe change the states enum type in OneButton.h from int to uint8_t (byte) and some others ? Can this be moved to a single byte as I stated above ?

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And also it is possible to create a setter method to change the number of the button pin while the program is running. For example we start with pin 2 and then change it to 3 ? I don't know if it's a great idea...

(sorry for my English, i'm French and i use google translate for write 🥴)

again thanks for your job!
Sincerely,
pandaroux007