Add no_optimize feature to disable optimizations.

Cargo.toml

@@ -26,6 +26,7 @@ no_stdlib = []      # no standard library of utility functions
 no_index = []       # no arrays and indexing
 no_float = []       # no floating-point
 no_function = []    # no script-defined functions
+no_optimize = []    # no script optimizer
 only_i32 = []       # set INT=i32 (useful for 32-bit systems)
 only_i64 = []       # set INT=i64 (default) and disable support for all other integer types