Merge pull request #42 from AntonGordienko/master

Added fetching GMail labels (X-GM-LABELS).
Fixed up formatting and some logic for the X-GM-LABELS feature
Use a list of strings instead of IFolders for X-GM-LABELS

The FolderCache will not necessarily have a mapping of all of the
user's folders, so using this will be unreliable. We also can't
send new commands to lookup/get the corresponding folders because
the command loop is not reentrant.

The easiest solution is to simply use a list of strings and have the
app deal with that.
Added support for searching for GMail labels
UTF-7 decode the GMail label names
Bumped verion to 0.12.0.0
Updated MailKit.nuspec
Added more IMAP examples
Make sure that DIGEST-MD5 realms are not null before dereferencing

Fixes issue #45 (many thanks to ckopas for digging into this)
Simplified the API by making CancellationTokens optional params
Bumped version to 0.13.0.0
Updated README.md for X-GM-LABELS status change
Update README.md
Sign the MailKit assemblies
Need to strong-name the UnitTests assembly as well
Only use the range of bytes specified when converting the token into a string
Fixed compile warnings in TargetInfo.cs
code cleanup
Catch SaslExceptions for SMTP and only throw them after falling back to other mechanisms

Fixes issue #47
Bumped version to 0.14.0.0