Consider surrogate pairs in replacing t.co to actual URL
Consider surrogate pairs in replacing t.co to actual URL

Because Substring method in System.String didn't consider surrogate
pair, incorrect replacing was happened if a tweet contained
Unicode surrogate pairs before URL.

Use SubstringByTextElements method in System.Globalization.StringInfo
instead of Substring method in System.String in case of surrogate pairs.

azyobuzin/Mystique,fin-alice/Mystique