Add _ReadSkipWhitespace, use it for Skip* methods
Use ReadSkipWhitespace() in trivial cases

ConsumeWhiteSpace + ExpectChar becomes ReadSkipWhitespace + CheckChar
Remove redundant end-of-stream check

ThrowExpected(c) is called if we don't match the expected char anyway,
so don't need explicit check for EOS.
Merge branch 'ReadSkipWhitespace'