Some points need to improve

[yjhmelody]

• We need to explore some ways to extract the ask! code from the as compiler internal. At present, it can be completely written as an independent ts project, in my personal opinion.
• We should define the metadata.json's spec class rather than generate it by template engine. It's hard to maintain and test it.
• The code in some places is hard-coded, and parameterization and configuration should be considered.
• Consider to add some prefix for contract decorator, for avoiding name conflicts.
• Add more unit tests.

[van-bright]

nice suggestions!