Add `-sort`

Fixes #34
Release 1.4.0
Add -sum function.
Add -product function.
Merge pull request #35 from rejeep/sum-and-product

Add -sum and -product functions
Release 1.5.0
Indent according to emacs lisp standard
Add -juxt
Add -min, -max, -min-by and -max-by.
Merge pull request #38 from rejeep/min-and-max

Add -min and -max.
Release 1.6.0
Fix typo

Closes #37
Actually update README :P