test(c_api): add C API testcases
chore(dsolvers/ode_solver.cpp): fix indentation
tests(nra_ode): use ode-order=35 for cardiac examples
fix(opensmt/api/opensmt_c.h): add interval value for mk_int_var/mk_real_var
fix(dsolvers/ode_solver): run prune_forward/backward only if SAT

fix #62
fix(dsolvers/ode_solver.cpp): print FATAL error message in case of ODE exception
fix(opensmt/egraph/EgraphStore.C): print full-precision in mkNum
feat(opensmt/egraph/EgraphStore.C): add more simplification

 - x ^ 1 = x  (mkPow)
 - 0 + x = x  (mkPlus)
 - x + 0 = x  (mkPlus)
 - x - 0 = x  (mkMinus)
 - 0 - x = -x (mkMinus)