Add AppVeyor continuous integration

[FarnazH]

There is a problem with iodata/molden.py on Windows due to file.seek() and file.tell() methods. This is because a different newline character is used on Windows, so seek does not take you back to the exact same place (beginning of the previously read line).

[FarnazH]

P.S. This is a problem with only Python 2.7 on Windows apparently because Python 3.5 and 3.6 changed the way file.seek() and file.tell() work.

[tovrstra]

We should probably rewrite the code not to use seek and tell. That is a rather fragile technique anyway.

[tovrstra]

P.S. I've updated the webhook to point to Roberto's account on AppVeyor.

[tovrstra]

This is the badge for appveyor:

[![Build status](https://ci.appveyor.com/api/projects/status/s1v03mj127dmoi7s/branch/master?svg=true)](https://ci.appveyor.com/project/theochem-ci-bot/iodata/branch/master)

When you push this a new commit (e.g. with the badge) it should start testing on appveyor as well.

[codecov]

Codecov Report

Merging #8 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master       #8   +/-   ##
=======================================
  Coverage   94.59%   94.59%           
=======================================
  Files          28       28           
  Lines        3087     3087           
  Branches      422      422           
=======================================
  Hits         2920     2920           
  Misses         82       82           
  Partials       85       85

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[tovrstra]

We'll fix the seek and tell later. Merging.