TestInjectedData works
TestLet works
TestGlobals, TestCss, change data.String.String() to single-quote
fix bug in CallParamValue, TestHelloWorld now works
Implement nullsafe navigation. TestDataRefs works.
all soyjs/exec tests pass
nullsafe initialization for opt_data only if all optional params
only generate ifempty code if necessary
remove unused quoteString
Use jSEscape rather than strconv.Quote
Refactor js render to temporary buffer