Implement split-stems

[jg20019]

This pull request implements split-stems.

If split-stems is true, then instead instead of use mod 10 to calculate the stems, it uses mod 5.
To calculate the base stem, it divides the stem by 2. For example with a vector #(10 15 16 18) by using mod 5 the stems become 2 3 3 3. When printing the stems it divides by 2 and gets the floor so both 2 and 3 are printed as 1.

Closes #2

[CLAassistant]

All committers have signed the CLA.

[Symbolics]

Thanks! I don't think that's what split stems is supposed to do. What split stems does is split (repeat) a stem if its values are too long. This PR looks like it divides the values of a single stem instead.

[jg20019]

I think I did it correctly. When I tried it with the data set from the example that you linked, I got the exact same result.

> (defvar numbers #(1 1 3 6 7 7 8 10 12 12 13 18 21 23 23 23 24 25 26 27 28 29 31 31 31 34 36))

> (stem-and-leaf numbers)
0 | 1 1 3 6 7 7 8
1 | 0 2 2 3 8
2 | 1 3 3 3 4 5 6 7 8 9
3 | 1 1 1 4 6  

> (stem-and-leaf numbers :split-stem t)
0 | 1 1 3
0 | 6 7 7 8
1 | 0 2 2 3
1 | 8
2 | 1 3 3 3 4
2 | 5 6 7 8 9
3 | 1 1 1 4
3 | 6

What could I be missing?

[snunez1]

You're right, that output is correct. Good work; if I'd known it was only a two line change I might not have asked for help. Thanks.