Keep DFDL 1.0 spec in step with ICU DecimalFormat class

[smhdfdl]

ICU DecimalFormat is where we derived our Figure 4 from. It says "ICU DecimalFormat aims to follow the specification for pattern strings in UTS #35. Refer to that specification for more information on pattern string syntax." Looking at that link, there appears to have been some enhancements or clarifications that we might need to incorporate into DFDL 1.0 specification. For example, minus sign as a symbol, and 'explicit plus' use of plus symbol. We need to do some tests to determine what needs to be updated.

Also, what does the text - special Characters and - quote signify in Fig 4? That is copied from DecimalFormat equivalent, but is not explained there either.

[mbeckerle]

These are new features that have been added to ICU; hence, do not need to be handled as an erratum, but can be added as DFDL v2.0 features.