Pwntools-elf-only

- [1784][1784] Use temporary cache directory when persistent cache cannot be used
- [1973][1973] ELF symbols can be looked up by bytes values
- several bugfixes ([2012][2012], [2031][2031], [1912][1912], [1961][1961],
[2007][2007], [2040][2040], [2051][2051])

[1784]: https://github.com/Gallopsled/pwntools/pull/1784
[1912]: https://github.com/Gallopsled/pwntools/pull/1912
[1961]: https://github.com/Gallopsled/pwntools/pull/1961
[1973]: https://github.com/Gallopsled/pwntools/pull/1973
[2007]: https://github.com/Gallopsled/pwntools/pull/2007
[2012]: https://github.com/Gallopsled/pwntools/pull/2012
[2031]: https://github.com/Gallopsled/pwntools/pull/2031
[2040]: https://github.com/Gallopsled/pwntools/pull/2040
[2051]: https://github.com/Gallopsled/pwntools/pull/2051

- [1733][1733] Update libc headers -> more syscalls available!
- [1876][1876] add `self.message` and change `sys.exc_type` to `sys.exec_info()` in PwnlibException
- [1877][1877] encoders error message handles when `avoid` is bytes in python3
- [1891][1891] Keep ROP gadgets when setting registers via setattr/call
- [1892][1892] Silence SIGPIPE error for "pwn phd"
- [1893][1893] Fix bytes warning in "pwn cyclic"
- [1897][1897] Add basic support for RISC-V
- [1903][1903] Add zsh completion script
- [1904][1904] Add bash completion script
- [1906][1906] Defer import of several modules to save on startup time
- [1921][1921] Add basic support for the bare-metal ARM specific toolchain
- [1995][1995] Add `shellcraft.*.linux.cat2`, which uses alloc+read+write instead of sendfile

[1733]: https://github.com/Gallopsled/pwntools/pull/1733
[1876]: https://github.com/Gallopsled/pwntools/pull/1876
[1877]: https://github.com/Gallopsled/pwntools/pull/1877
[1891]: https://github.com/Gallopsled/pwntools/pull/1891
[1892]: https://github.com/Gallopsled/pwntools/pull/1892
[1893]: https://github.com/Gallopsled/pwntools/pull/1893
[1897]: https://github.com/Gallopsled/pwntools/pull/1897
[1903]: https://github.com/Gallopsled/pwntools/pull/1903
[1904]: https://github.com/Gallopsled/pwntools/pull/1904
[1906]: https://github.com/Gallopsled/pwntools/pull/1906
[1921]: https://github.com/Gallopsled/pwntools/pull/1921
[1995]: https://github.com/Gallopsled/pwntools/pull/1995

- [1429][1429] Add a mechanism for ret2csu (originally 1138)
- [1566][1566] Add `ignore_config` argument to `pwnlib.tubes.ssh` and improve `allow_agent` implementation
- [1652][1652] Add `process.readmem` and `process.writemem`
- [1739][1739] Add/fix shellcraft.linux.kill() / shellcraft.linux.killparent()
- [1746][1746] Prefer Python3 over Python2 for spawning remote processes over SSH
- [1751][1751] Fix process() with executable relative to cwd
- [1753][1753] major change: less unconditional imports in pwnlib
- [1776][1776] mips: do not use $t0 temporary variable in dupio
- [1846][1846] support launching GDB in more different terminals

[1429]: https://github.com/Gallopsled/pwntools/pull/1429
[1566]: https://github.com/Gallopsled/pwntools/pull/1566
[1652]: https://github.com/Gallopsled/pwntools/pull/1652
[1739]: https://github.com/Gallopsled/pwntools/pull/1739
[1746]: https://github.com/Gallopsled/pwntools/pull/1746
[1751]: https://github.com/Gallopsled/pwntools/pull/1751
[1753]: https://github.com/Gallopsled/pwntools/pull/1753
[1776]: https://github.com/Gallopsled/pwntools/pull/1776
[1846]: https://github.com/Gallopsled/pwntools/pull/1846