Add support for SSMS 18

[EWSoftware]

SSMS 2018 removes the restriction that extensions be whitelisted thus getting rid of all the hacks needed to install third party extensions. See if the spell checker can be updated to install in it.

https://www.codeproject.com/Articles/1377559/How-to-Create-SQL-Server-Management-Studio-18-SSMS
https://social.msdn.microsoft.com/Forums/vstudio/en-US/4ddb7214-c3d1-440d-8774-61751fec63b3/can-i-install-a-ssms-extension-with-the-vsix-installer?forum=vsx

[EWSoftware]

While the package is loaded and the configuration editor works, the SSMS editor uses a different method of editing files and does not invoke the taggers like Visual Studio. As such, spell checking in the editor isn't supported and there doesn't appear to be a way to enable it.

It may be better to add some form of specialized spell checking that can be invoked from Visual Studio using the Server Explorer tool window.