Minor Math Sum Additions (#2007)

* Move sum tests into math directory

* Move sum documentation over to math documentation

One sum example already existed in the math examples and a few of the others were outdated and didn't work, so I only moved one over, and updated their output

* Remove no-longer-in-use mod statement

docs/commands/math.md

@@ -117,6 +117,13 @@ To get the average of the file sizes in a directory, simply pipe the size column
 ────────────┴────────
 ```
 
+To get the sum of the characters that make up your present working directory.
+
+```shell
+> pwd | split row / | size | get chars | math sum
+50
+```
+
 ## Errors
 
 `math` functions are aggregation functions so empty lists are invalid