Implement PrivateSymbol.isPrivateSymbol
Move call opcodes to lv5/breaker/compiler_call.h
Optimize cmp(reg, 0) to test(reg, reg)

Thanks to @herumi, we reduced machine code bytes :)
Remove wasted string allocation
Fix OP::ENTER in breaker
Refactoring Date implementation

Cleanup and make them faster
Update MSVC macro
Refine String#substring implementation code
Merge branch 'master' into breaker