Use a library to parse custom syntax in arguments

[piodul]

The c-s and s-b frontends have some parameters with custom syntax. Currently, they are all parsed using ad-hoc routines that manipulate on strings, which are tedious to write and hard to read. We should consider pulling in a parsing library and defining the syntaxes of the parameters in a declarative way.

When choosing the library, we should optimize for code readability and clear error messages. The performance is completely irrelevant as parsing only happens at the program start.