Add history exclusion configuration

[rgwood]

A rough draft PR to solve #516, by letting users configure which command lines get excluded from history. For example, users can configure reedline so that command lines starting with a space are not saved.

@sholderbach Let me know what you think, happy to revise this.

[sholderbach]

Doing the string match internally is certainly the minimally invasive change. How will this interact with the data amending as done for the sqlite history?

[rgwood]

@sholderbach I don't think there's any special handling for SQLite history needed, because all the logic is happening in engine.rs. Perhaps I've missed something?

[sholderbach]

Starting the session without a normal command being run crashes, as soon as I try to add an entry that is skipped (with --features sqlite):

I think it tries to modify the last entry (and passes if it can mess with the last succesfully stored one)

[rgwood]

Oops! Will take a look and try to add some tests, thanks.

[rgwood]

Hm. Y'know, I'm not sure whether that's a bug. A case could be made that the demo is intentionally not handling that edge case (where the very first command is ignored) well:

reedline/examples/demo.rs

Line 130 in 076ce6f

.expect("todo: error handling");

Do you have a suggested way forward?

[sholderbach]

I think this rather indicates even with ignoring error handling that https://docs.rs/reedline/latest/reedline/struct.Reedline.html#method.update_last_command_context would try to modify the last remembered entry.

[rgwood]

Right. I don't see the problem but I'm probably missing something.

edit: Oh, I think I get it now. I guess we might modify the wrong entry. :(

[rgwood]

current status: I'm not really sure what the best way to implement this is. Might need to start storing the last command in memory instead of always looking it up in the DB. I've run out of steam to work on this for now but might come back to it another time; if anyone else wants to pick it up feel free.

[sholderbach]

Closed by #566