Run 'make test' in single-threaded mode.
valueOf()/toString()/Boolean() improvements.

Also implemented [[toObject]], [[toPrimitive]], [[toString]], [[toBoolean]],
[[toNumber]], [[DefaultValue]] internal methods.  Fix ''*1 case. Add tests.

Updated turtlescript standard library to match turtlescript commit
22a0ae6b6e0792c13ba6308f616ab9b3d5b6a972.