Fix handling hex numbers in expression

[gmelchett]

Make code like this work:

    vars := map[string]interface{}{"addr": 0x1000}

    value, err := gval.Evaluate(`addr == 0x1000`, vars)

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Signed-off-by: Jonas Aaberg cja@lithops.se

[generikvault]

Hi gmelchett,

thank you for contributing. I can accept the pull request if you fix the following issues:

• parse for hex if the value starts with 0x
• update the documentation in the readme about numeric constants
• add a test for hex values
• fix the TestParsingFailure test for incorrect hex numbers

kind regards

GeneriK