Merge #67

67: Fix register configuration and documents r=Disasm a=luojia65

This pull request contains:

1. Use `#[cfg(target_pointer_width = "32")]` other than `#[cfg(riscv32)]` to provide support on IDE lint and cargo doc outputs
2. Add `#[inline]` on most of `set` and `write` functions


Co-authored-by: luojia65 <me@luojia.cc>
Co-authored-by: Luo Jia <me@luojia.cc>