F# Make build script

I replaced the existing psake scripts with F# Make build.fsx script. It support source indexing using my SourceLink add on and builds using AppVeyor.

You can see some builds I made here:
https://ci.appveyor.com/project/ctaggart/burrows/history

After merging the pull request, you just need to change the url in build.fsx to be raw.githubusercontent.com/eswann/burrows.

To make the stable build using AppVeyor, I just set `fakeargs` temporarily in the UI to `nuget versionAssembly=0.3.1.1 versionFile=0.3.1.1 prerelease=`.
![image](https://cloud.githubusercontent.com/assets/80104/3335285/d275cbd0-f810-11e3-8c48-196f73e1d638.png)