Include api documentation

Adds XML (intellisense) documentation to the build output
Merge pull request #18 from gregmac/patch-1

Include api documentation
Added BSD license
Handle possible Nullref in SentryStacktrace

frame.GetMethod().DeclaringType can be null, this patch handles that
Merge pull request #19 from gregmac/patch-2

Handle possible Nullref in SentryStacktrace
Add some basic resource links
Remove obj files
Fix NullRef on empty stacktrace