Fix for underscore emphasis when followed by punctuation

Hello,

An issue was identified (#25) where underscore emphasis was not being converted to HTML correctly if followed by punctuation.

#### Example:
`_internal_,` would be incorrectly rendered to `_internal_,`, when the expected output is `<em>internal</em>,`.

I added a test for this and implemented a fix for both the C# (43baf230629d8901a7e69c4ec17a35884e03a27b) and JavaScript (43792317721c2023e91db27d935eda87c6b8eeb7) projects.

I made a few changes that are unrelated to the fix, which are optional to merge:

- Updated .gitignore, added .gitattributes
- Updated project to VS2012
- Updated NuGet and enabled NuGet package restore

Thank you for your work with MarkdownDeep, it is an excellent library. Please feel free to contact me if you have any questions or feedback.

Best regards,

Evan