v0.9.0 Support more syscalls

Merge pull request #17 from TheWaWaR/add-ckb2021-syscalls

feat: add ckb2021 syscalls: vm_version, current_cycles, exec

v0.8.0 Support ckb2021

Merge pull request #16 from TheWaWaR/support-ckb2021

chore: support ckb2021

v0.7.4

• Upgrade ckb-c-stdlib

v0.6.2

• Fix InvalidElf error 0f4de4c

v0.3.0

• Use mixed allocator as default allocator https://justjjy.com/ckb-std/riscv64imac-unknown-none-elf/doc/src/ckb_std/global_alloc_macro/default_alloc.rs.html#1-43
• Remove LibC allocator macro

v0.2.2

• Add a new batch of high-level syscall Apis, located in the high_level module.
• Add a new QueryIter advanced API for in batch operation on cells/headers/witnesses/inputs.
• debug! is disabled in the release build.
• Release documentation