Use host func to determine unsupported opcodes

[qizhou]

Since we only compile the perf-related opcodes, whose gas prices are stable, we can defer the rest opcodes, including unsupported ones, to the host function so that we can support the forks in the future easily.

[qizhou]

In addition, for gas consumption, the compiled code may only account for those stable opcodes, and use the host function to evaluate the rest ones.

[qizhou]

Related to #11 , #56

To be more specific, we should

• add a field of opcode to indicate whether it will be compiled to native code (true) or via host func (false)
• The compiler will check the field: if the field is false, then it will call the host function, where the host function will charge both constant gas and dynamic gas; or if the opcode is not supported, the host function will return error.