ENH: region-wise decomposition specification for decomposeParDict
Within decomposeParDict, it is now possible to specify a different decomposition method, methods coefficients or number of subdomains for each region individually. The top-level numberOfSubdomains remains mandatory, since this specifies the number of domains for the entire simulation. The individual regions may use the same number or fewer domains. Any optional method coefficients can be specified in a general "coeffs" entry or a method-specific one, eg "metisCoeffs". For multiLevel, only the method-specific "multiLevelCoeffs" dictionary is used, and is also mandatory. ---- ENH: shortcut specification for multiLevel. In addition to the longer dictionary form, it is also possible to use a shorter notation for multiLevel decomposition when the same decomposition method applies to each level.