Merge pull request #48 from fogzot/master

Removal of Mono.Data.Sqlite dependency
Modified DbExtensions.CreateParameterWithValue() to be DbExtensions.AddParameterWithValue()
Don't use reflection for Mono.Data.Sqlite for Xamarin mobile platforms
Added a new .ctor to DefaultSecureMimeContext and made SqliteCertificateDatabase public
Documented most of the newly exposed X509 certificate database APIs
Finished documenting all of the new database APIs
Added a work-around for mail clients that mistakenly quote rfc2184 encoded parameter values

Fixes issue #49
Added more runtime checks to make sure Mono.Data.Sqlite will work
Bumped version to 0.32.0.0
Removed sqlite3.dll and Mono.Data.Sqlite from MimeKit.nuspec
Updated unit tests
Documented how to register your own CryptographyContexts
Allow parsing of message with 0 byte body.
Merge pull request #51 from hultqvist/master

Allow parsing of message with 0 byte body.
Cleaned up previous pull request a bit and added some commentary
Fixed compile warning by commenting out one-pass stuff that we don't use
Added a unit test for issue #51 and fixed it to actually work
Switch to using PBE SHA-256 + AES256 for encrypting private keys instead of SHA-1 + 3-key TripleDES
Added support for PostgreSQL-based certificate database

* Abstracted common SQL code in new class SqlCertificateDatabase.
* Fixed SQL to not use SQLite-only syntax (explicit lower() calls instead
  of COLLATE NOCASE, "IS NOT NULL" instead of just "NOT NULL")
* Fixed certificate loading to not depend on case of column names (some
  backends implicitly convert uppercase to lowercase unless the
  identifiers are quoted and return column names with different case than
  the one used in CREATE TABLE).
* Added NpgsqlCertificateDatabase class and tests.