Fix examples of opaque types

[panacekcz]

The bug in Logarithm was reported by @wks on gitter.

Perhaps in both cases, it is not obvious that the operator on the right hand side is the one from the underlying type.
Especially in the second case, where ReadWrite must be defined as ReadOnly | WriteOnly inside Access, but the equivalent defined outside Access would be ReadOnly & WriteOnly.

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[panacekcz]

Explanation:

1. the * in LogarithmOps adds two logarithms to compute multiplication of two numbers. The result of such addition is a logarithm of the product, so it should be converted from Double to Logarithm directly, without applying math.log to it.
2. The ReadWrite value in Access must use the | operator on the underlying integers of Read and Write to compute a value with both bits set. Using & on the underlying integers would make the value 0, which would be the same as NoPermission.
   Similarly, the & operator must use | operator on the underlying integers.

The continuous-integration failure does not seem to be related to this fix.

[odersky]

This somehow fell through the review cracks. Anyway, looks all good. Thank you for the fixes.