Use external string resource for strings longer than or equal to 128 characters when creating v8 strings from NSStrings.
m Make L8Value have a strong reference to the v8 value by using a persistent storage. Now, as long as the L8Value is references, it has a strong reference to the v8 value so it is not GCd. Send isolate as argument to all objectToX and valueToX functions for better performance. Build v8 as Debug with GDBJIT by default (see v8_build.sh).