Parsing error on hexadecimal character reference in attribute value

[bfreuden]

When parsing the following xml:
<root att="&#xA;"></root>

The parser fails with the following error:

com.fasterxml.aalto.WFCException: Unexpected character 'A' (code 65) expected a hex digit (0-9a-fA-F) for character entity
at [row,col {unknown-source}]: [1,16]
at com.fasterxml.aalto.in.XmlScanner.reportInputProblem(XmlScanner.java:1333)
at com.fasterxml.aalto.in.XmlScanner.throwUnexpectedChar(XmlScanner.java:1498)
at com.fasterxml.aalto.async.AsyncByteArrayScanner.handleHexEntityInAttribute(AsyncByteArrayScanner.java:4198)

The parser does not seem to support hexadecimal character references not starting with [0-9] although it is allowed by the XML specification.

I will issue a pull request shortly containing a fix proposal with a JUnit test case.

PS: as it is my first comment here, thanks a lot for this great library!