Run tests during AppVeyor builds

[jariq]

Part of #45 - AppVeyor configuration needs to be adjusted.

[jariq]

Per platform notes:

• net20 - All tests are executed with 32-bit unmanaged PKCS#11 library.
• net40 - All tests are executed with 64-bit unmanaged PKCS#11 library.
• net45 - No tests are executed because they would essentially be the same as for net20 and net40 platforms.
• sl5 - No tests are executed because they run in MSIE and require rather complicated OS setup and code signing certificate.
• netstandard1.3 - All tests are executed with 64-bit unmanaged PKCS#11 library but test results are not displayed in AppVeyor web interface.
• monoandroid2.3.bat - No tests are executed because they require Android device or simulator.
• xamarinios1.0 - No tests are executed because they require iOS device or simulator.