Add additional matchers

[tschuchortdev]

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Adds some additional matchers like not, or leq. I couldn't be bothered to write tests because the code is so incredibly simple.

[perkss]

Any plans to put this in?

[TWiStErRob]

@tschuchortdev the code is simple, but it's still code, and the tests would protect it from breaking in the future. For example, if the functions get reordered, and accidentally change bodies or something we don't know yet. Verifying a basic requirement that the function delegates to the right one (by validating what it does e.g. tests would be different for lt and leq).