Summary
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Explicitly specify the behavior of `Reader.skip(long)` at end-of-stream.

Problem
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The specification of the behavior of `Reader.skip(long)` at end-of-stream is insufficiently clear to some readers. For example some could think that -1 is returned if the method is invoked when the reader is already at end-of-stream.

Solution
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Update the specification of `Reader.read(long)` and its overrides to specify clearly the behavior at end-of-stream.

Specification
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A normative specdiff and a webrev are attached.

The text of `Reader.skip()` is updated and the subclasses inherit all or part of this text. In subclasses which have only

    /**
     * {@inheritDoc}
     */

as the specification of `skip(long)`, the method will no longer appear in the main method summary, but rather in the section "Methods declared in class java.io.Reader". This is the case for `BufferedReader`, `LineNumberReader`, and `PushbackReader`. The specifications of `skip(long)` in the other subclasses add some value however so their verbiage is not entirely inherited. `FilterReader` provides different text for its `@throws` clause for `IllegalArgumentException`, while `CharArrayReader` and `StringReader` provide their own verbiage except for their `@param`, `@return`, and `@throws` tags which inherit their respective descriptions.