Target filter

I want to be able to run this:
```shell
sshtool -f targets.file -t '*10??*' 'echo this will run on every AWS SCIONLab host'
```
Or this
```shell
# Grab the targets from the .ssh directory and filter out those that are not *10??* :
sshtool -t '*10??*' 'echo this will run on every AWS SCIONLab host'
```

Write a filter that accepts text and regular expressions do enable this feature.
