Add emission of published files

[Niksko]

This adds an option which allows you to emit published to the stream. This is incredibly useful because it neatly encapsulates publishing your code to a temporary directory and then returning a stream of the published files. This makes it easy to pipe the stream into other gulp plugins to perform further work on the published files.

As discussed in issue #46, this adds the following functionality:

• an emitPublishedFiles option which causes the published files to be emitted by the plugin. Setting this to true causes the required msbuild options to be added to the msbuild command that enables a filesystem publish to a the provided directory
• an accompanying option, publishDirectory which controls where the files are published to on the filesystem. If this option is not specified, the publishDirectory defaults to a directory inside the system temp folder, with a folder name based on a uuid v4

I have added some unit tests of this functionality, but feel free to suggest more.

[coveralls]

Coverage increased (+0.2%) to 98.773% when pulling 58b432a0cd835015a75a0eedde99422f41ce5e1e on Niksko:master into a549abc15849266756de03e0f144c17e67a60101 on hoffi:master.

[coveralls]

Coverage increased (+0.2%) to 98.773% when pulling 58b432a0cd835015a75a0eedde99422f41ce5e1e on Niksko:master into a549abc15849266756de03e0f144c17e67a60101 on hoffi:master.

[coveralls]

Coverage increased (+0.2%) to 98.773% when pulling 58b432a0cd835015a75a0eedde99422f41ce5e1e on Niksko:master into a549abc15849266756de03e0f144c17e67a60101 on hoffi:master.

[Niksko]

Apologies, this should probably be a PR into develop