Add git attributes for line ending and merging

Default .NET development gitattributes file for proper merge and line
ending handling
Update .gitignore to GitHub recommendation

Using https://raw.github.com/github/gitignore/master/CSharp.gitignore
Remove Files to be excluded from new ignore file
Exclude pkg and objpkb
Merge pull request #2 from nschonni/add-gitattributes-for-line-endings

Add gitattributes for line endings