Improvements to the Ada lexer

[jcprpr]

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There are some simple changes that could be done to improve the Ada lexer:

1. Ada is not case sensitive.
2. Ada 2022 added the reserved word parallel. Additionally, apparently the reserved words overriding and some were missing. Here is a full list.

Also, you might want to fix privilages -> privileges on the textadept homepage.

[orbitalquark]

Thanks for the heads up, I will look into this when I have some time.

[orbitalquark]

Ada improvements were committed in Scintillua: https://github.com/orbitalquark/scintillua/commit/9fd3ed6d4f13458a11a8fc38dd6aa3ded72f3c48.