There is no need to use such an old `idna` version.
The latest works with py35+ and all tests pass.
Newer `idna` supports the latest Unicode standard and latest python
versions.
https://github.com/kjd/idna/blob/master/HISTORY.rst
cryptography 41.0.0 crashes warcprox with the following exception:
```
File "/opt/spn2/lib/python3.8/site-packages/warcprox/main.py", line 317, in main
cryptography.hazmat.backends.openssl.backend.activate_builtin_random()
AttributeError: 'Backend' object has no attribute 'activate_builtin_random'
```
Also, cryptography==40.0.0 isn't OK because when I try to use it I get:
```
pyopenssl 23.2.0 requires cryptography!=40.0.0,!=40.0.1,<42,>=38.0.0, but you have cryptography 40.0.0 which is incompatible.
```
So, the version should be <=39.0.0
cryptography 41.0.0 crashes warcprox with the following exception:
```
File "/opt/spn2/lib/python3.8/site-packages/warcprox/main.py", line 317, in main
cryptography.hazmat.backends.openssl.backend.activate_builtin_random()
AttributeError: 'Backend' object has no attribute 'activate_builtin_random'
```
Also, cryptography==40.0.0 isn't OK because when I try to use it I get:
```
pyopenssl 23.2.0 requires cryptography!=40.0.0,!=40.0.1,<42,>=38.0.0, but you have cryptography 40.0.0 which is incompatible.
```
So, the version should be <=39.0.0
If connection to a hostname:port fails, add it to a `TTLCache` with
60 sec expiration time. Subsequent requests to the same hostname:port
return really quickly as we check the cache and avoid trying a new
network connection.
The short expiration time guarantees that if a host becomes OK again,
we'll be able to connect to it quickly.
Adding `cachetools` dependency was necessary as there isn't any other
way to have an expiring in-memory cache using stdlib. The library
doesn't have any other dependencies, it has good test coverage and seems
maintained. It also supports Python 3.7.
