Documentation improvements

This project helped me considerably and I felt I wanted to express my
appreciation in some way, so I decided to improve the documentation.

I have tried to keep each commit as 'atomic' as possible, for example 64dc298
only corrects the spelling and grammar, while f504643 modifies the example code
slightly to include error handling. As a note, you may want to think carefully
about d13fa15 as it changes your citation slightly.

Also, in [index.rst#Contact](http://pythonhosted.org/PyDAQmx/index.html#contact), would you like to link to the GitHub issues page?

I am willing and eager to check and improve the text in `setup.py`, but first
the two versions need to be consolidated into one as the content is slightly
different. Maintaining two copies of a large block of text is unwise,
especially since it is due to only one word. Either save it as a variable and
use string interpolation/concatenation or properly encode/decode the text as
required. Please let me know when this is done and I will check the text for
you.

Let me know if you would like any further clarification on any of the commits.