doc(README.md): add coverity scan badge
fix(opensmt/smtsolvers/SMTConfig.c): assign initial value to nra_json (false)
fix(opensmt/smtsolvers/SMTConfig.c): assign initial value to nra_ODE_timeout (0.0)
fix(opensmt/smtsolvers/SMTConfig.c): assign initial value to nra_ODE_timeout (0.0)