Mono building & Continuous Integration

This pull request was prompted by
<blockquote class="twitter-tweet" lang="en"><p>The challenge to build <a href="https://t.co/V4XTh0Dz0w"> https://code.google.com/p/google-api-dotnet-client</a> using Mono on OSX remains open. Your chance to prove that I really have a peanut-sized brain!</p>&mdash; Erik Meijer (@headinthebox) <a href="https://twitter.com/headinthebox/statuses/455624948238020608">April 14, 2014</a></blockquote>

However, if changes were made without continuous integration, mono support would just break again, so I mirrored google-api-dotnet-client to github using [git-remote-hg](https://github.com/git/git/blob/master/contrib/remote-helpers/git-remote-hg), so I could include in my pull request [travis-ci](https://travis-ci.org) and [appveyor](http://www.appveyor.com) configs, both free for open source. I'd be happy to transfer this repo to @peleyal if he'd like to gain these benefits moving to git and github (like [google/google-api-php-client](https://github.com/google/google-api-php-client), [google/google-api-nodejs-client](https://github.com/google/google-api-nodejs-client), or [google/google-api-ruby-client](https://github.com/google/google-api-ruby-client))

This pull request contains in itemized commits:
  * some git specific configuration
  * updates nuget.exe to a mono compatible version
  * adds an [FSharpMake](http://fsharp.github.io/FAKE/)File to avoid multiple .sln files and platform specific scripts
      * `./build.fsx` on mac or linux
      * `fsi --exec build.fsx` on win
  * switches the portable projects to mono compatible Profile 136 (bumps min version Silverlight 4->5 and Windows Phone 7.1->8)
  * Adds Mono (Mac) CI [![Build Status](https://travis-ci.org/jbtule/google-api-dotnet-client.svg?branch=mono-building)](https://travis-ci.org/jbtule/google-api-dotnet-client) and Windows 2012 Server CI 
[![Build status](https://ci.appveyor.com/api/projects/status/2s20kh42qioi6hbf)](https://ci.appveyor.com/project/jbtule/google-api-dotnet-client)
  * Changes some assertions to be more cross platform friendly