Drop everything from v1 and recreate the framework to v2!

[onevcat]

Rewrite everything from scratch. Now only the name keeps the same. XD

Changes

• Pure Swift implementation. No libpng or black box anymore.
• This should fixes almost all issues opened. But I will then check them one by one again.
• Drop the internal image cache, which not transparency to external users and error-prone.
• High performance loading and streaming data.
• Fully APNG spec and passing all APNG testing cases.