 Encode an index of a [nibble](https://en.wikipedia.org/wiki/Nibble) from a u64 as a u8.
 
 `|      4 bits     |     4 bits     |`
 
 `| index of nibble | nibble of data |`
 
 # Usage
 
 ```rust
 use crate::CrumbExt;
 
 fn main() {
     let test: u64 = 0b11111111;
     // let crumb: u8 = unsafe { test.get_unchecked_crumb(1) };
     let crumb: u8 = test.get_crumb(1).unwrap();
     assert_eq!(0b11110000u64, u64::from_crumb(crumb));
 }
 ```
 
 ### Name
 
 A nibble of something is about the size of a crumb or something like that...
 
 ### How?
 
 Was doing some research on variable length integers and realized how nicely this fits.
 
 ### Why?
 
 I don't think there are too many applications for this, I have one in mind but that is an entire project in itself.