Support the f2003 parser

[rupertford]

The f2003 parser in fparser parses to a lower level than the (default) parser. This lower level is required to be able to effectively analyse allocate statements, which is one of my short term aims. Therefore we need to be able to use the f2003 parser in this code. Hopefully we will be able to write something that allows us to choose which parser we want whilst keeping the core fanalyser the code the same in both cases.