Unless specified otherwise, operators in Haskell associative to the
left. However, the ergonomics of (!>) heavily lean towards the left
operand being a "single" search engine, not a combined one.
This causes trouble when not using `multi` or defining search engines
with a right fold, but (following the documentation) writing something
like
multiEngine = intelligent (wikipedia !> mathworld !> (prefixAware google))
instead. This particular definition would force the user to write
`wikipedia/mathworld:wikipedia:search-term` instead of just
`wikipedia:search-term` to access the first search engine.
Simply giving (!>) an explicit associativity fixes these problems.
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