FR: support environment variables in (favourite) queries

I'd love to see support for using environment variables in favourite queries, or even in all queries.

The use case is that I have several very similar databases where favourite queries all need to take a parameter to indicate what 'variant' of the database I'm currently using, _or_ I have to copy configuration files for each database file and alter one value in each query filter.

Say, the different values are `'foo'` and `'bar'`, and I have to either do:

```ini
favquery1 = '''select ...
from some_table
where parameter='$1'
and other_paramater='$2'
'''
favquery2 = '''select ...
from some_other_table sot inner join a_third_table att on sot.id = att.sot_id
where sot.parameter='$1'
and att.column_name ='$2'
'''
```

and then run `\f favquery1 foo 42` and `\f favquery2 bar 45`, **or** I copy the configuration file multiple times and hardcode the parameter in each.

If, instead, I could use environment variables (syntax suggestion, feel free to come up with better syntax, this is based on bash):

```ini
favquery1 = '''select ...
from some_table
where parameter='${PARAMETER}'
and other_paramater='$1'
'''
favquery2 = '''select ...
from some_other_table sot inner join a_third_table att on sot.id = att.sot_id
where sot.parameter='${PARAMETER}'
and att.column_name ='$1'
'''
```

and then start each `litecli` instance with a different environment variable and use the exact same favourites for each database:

```sh
$ PARAMETER=foo litecli foo_database.sqlite
foo_database.sqlite> \f favquery1 42
```

and

```sh
$ PARAMETER=bar litecli bar_database.sqlite
bar_database.sqlite> \f favquery1 42
```