Improved ODE/DAE support

by dantexid for ASCEND

The project implies creating a library using LINK semantics, to better describe dynamical systems. For this purpose, the Ascend language parser will need to be extended. I will use Bison, using on a context free grammar defined for this purpose, to create a C programs that parse a given input based on that grammar. Flex will also be useful to scan for specific lexical patterns in the input (a satisfactory structure for ODEs and DAEs must be defined).