Allow inputing specs using a human-friendly concrete syntax

[grayswandyr]

To allow easier experiments with Pardinus, we could add a human-friendly concrete syntax, thus removing the obligation to use the Java API. I am advocating a syntax akin to that of E. Torlak's PhD thesis and articles. The electrod input syntax (example) roughly follows these lines and could serve as an inspiration. The corresponding grammar should belong to a nice grammar class. ANTLR seems to be the way to go these days.

Seems like a good student project.