Update README.md - small typo

As part of my day job I review policies and standards, and this one came up recently. Small, but very common typo.
Merge pull request #882 from curtisk/patch-1

Update README.md - small typo
Name the arithmetic operators, including modulo, in the Reference

I write the name of the “modulo” operator because I wanted to know how to do it in Sass, but couldn’t find out by searching the Sass Reference. Searching for `%` didn’t help, since that character is used all over in percentages.

I added the names of the other operators because the list would look weird if only one of the operators were named. And I suppose somebody might want to search for “division”, if they noticed that `/` is already used in CSS and wondered if Sass used a different character for division.
Fix redundancy in documentation for hsla function arguments
Add warning that recursion is forbidden to the Sass Reference

This documents the limitation I stumbled upon when writing a mixin.

Closes #897
Merge pull request #898 from roryokane/patch-2

Name the arithmetic operators, including modulo, in the Reference
Merge pull request #900 from jackie/stable

Fix redundancy in documentation for hsla function arguments
Add a Map data type.

There are currently no operations for it.
Make list functions work for maps.

This adds Tree::Value#separator as a more generic way of getting the
separator of a SassScript value, since now maps notionally have a
separator as well.
Make empty lists function as empty maps as well.
Add SassScript functions for manipulating maps.
Support destructuring in @each.
Add reference docs for maps and @each.
Add a changelog entry about maps and @each.
Allow lists of pairs to be passed to map functions.

This is immediately deprecated.
Expose the Sass stack to the environment and thus to Sass functions.
Display a stack trace for the pairs-as-maps deprecation warning.
Merge branch 'stable'

Conflicts:
	lib/sass/script/functions.rb
Merge branch 'maps'

Closes #642