v0.3.0 (for Assemblyscript v0.25)

• Refactor internal implmentations to adapt to Assemblyscript v0.25.
• Rewrite some transform logic to adapt to Assemblyscript v0.25.
• Add more abstract methods to Core Serde.
• Now support dynamic class to be ser/deser.
• Fix test cases that failed in Assemblyscript v0.25.

In total, the ability of serde-as is not weakened, and even has a simple enhancement.

Note: Some behaviors may be changed but still not clear for user(even for me).