expose typeof via emscripten::val
fix looptemp replacements when there is a continue with a phi of the loop variable
Merge pull request #2360 from chadaustin/expose-val-typeof

expose typeof via emscripten::val
Add new functions AsciiToString, stringToAscii, UTF8ToString and stringToUTF8 to complete the set of string marshalling functions.
Optimize Pointer_stringify to use UTF8ToString and AsciiToString
Merge stringToAscii and writeAsciiToMemory.