[ESS] iESS - consistent string formatting within single and double quotes

[Steven McKinney]

OT and with apologies...

> So for the text string
>       .... a second order Taylor series about it's value at ....
> the color changes to red at the single quote mark an persists until the
> next one.  

It's, being a contraction of "it is", perhaps requires
an emacs lisp macro to expand it.  Resultant sentences such
as 

.... a second order Taylor series about it is value at ....

would alert users as to improper use of the apostrophe,
as well as leaving the emacs buffer coloured appropriately,
a doubly useful side effect :)

The Apostrophe Police