Added in 'auto' as an available value on margins

.mha replaces having a class to center block-level elements in a container. The rest are added to make this a complete set.
.pop module doesn't look right, fix it
Merge pull request #137 from seansoong/fix-pop-module

.pop module doesn't look right, fix it
Removed the unnecessary declarations

margin-top:auto; and margin-bottom:auto are the same as margin-top:0; and margin-bottom:0;
Merge pull request #113 from mindofmicah/master

Adding "auto" to acceptable margin values
Remove old files
New components and build tool
Merge pull request #157 from mobywhale-chan/master

New components and build tool
remove useless folders and files
Merge pull request #159 from arnogues/master

Remove vagrant folder
Update README.md
Update README.md
Update _pxToEm.scss

Added a check for if the value 'auto' is passed to the function to deal with cases where auto is desired as an output.  for example:

margin: pxToEm(20px auto, 16px); would output -> margin: 1.25em auto;
Merge pull request #163 from MrFjords/patch-1

Update _pxToEm.scss
Update _table.scss
Add condition around divider class name