brk done

Fix: `MemorySet::find_free_area` does not respect lower limit

* use local `memory_addr` for `memory_set`, update `memory_set`, move generic params of mapping structures into `MappingBackEnd` as associated types

* fix docs

* Enhanced `MemoryAddr` (#4)

* demo: what if we add more bounds to `MemoryAddr`

* remove arithmetic bounds for `MemoryAddr`, add some provided methods

* rename `MemoryAddr::sub_addr` to `MemoryAddr::offset_from`

* remove a wrong bug todo

* add two more functions to `VirtAddr`

* add `add` and `sub` to `MemoryAddr`

* clarify the behavior of arithmetic operations of `MemoryAddr`, add detailed unit tests

* formatted

* add `overflowing_add/sub` to `MemoryAddr`

* add `checked_add/sub` to `MemoryAddr`

* `AddrRange` candidate B: allow malformed ranges and treat them as empty

* doc and tests improvement for `MemoryAddr` and `AddrRange`

* update `PageIter`

* formatted

* even more tests, ready to merge

* switch to `AddrRange` candidate A

* add `sub_addr` series to `...

Add `MemoryAddr` trait, add `AddrRange` struct, use macro to generate `PhysAddr` and `VirtAddr` (#1)

* add `MemoryAddr` trait, use macro to generate `PhysAddr` and `VirtAddr`

* loosen the bound of `MemoryAddr`, move functions about alignment back to `PhysAddr` and `VirtAddr`

* update `def_addr_type!` to a better version, only `usize` supported now

* fix formatter for address types generated by `def_addr_types!`

* add `AddrRange`

* export `AddrRange`

* rename `def_addr_types!` to `def_usize_addr!`, and give it a new syntax

* i love `///`

* re-add mistakenly removed `as_ptr` and `as_mut_ptr` to `VirtAddr`

* add doc comment to `VirtAddrRange` and `PhysAddrRange`

* doc improvement

* add a new `#[inline]`

* move impl for `Debug`, `LowerHex`, and `UpperHex` from `def_usize_addr!` to a new macro named `def_usize_addr_formatter!`, which accepts custom formatter, in order to keep consistency with the original `Virt/PhysAddr::fmt`

* doc fixed

* update `Debug` impl for `AddrRange`, add `LowerHex` and `UpperHex` impl for `AddrRange`

* a small doc fix about number of `#`s

* a small doc fix

* doc and fixes about `def_usize_addr!` and `def_usize_addr_formatter!`

* change doctests for `AddrRange`

* doc fix

* replace `VirtAddrRange` with `AddrRange<usize>` in doc tests for `AddrRange`

* hidden `fn main` in doc test of `def_usize_addr`

* replace `VirtAddrRange` with `AddrRange<usize>` in doc tests for `AddrRange`

Protect memory mappings