Add history_filter setting to exclude commands from history

[jbaiter]

Adds a new history_filter setting through which users can specify a list of regular expressions that match commands that should not be recorded in the history.

Example configuration:

## prevent commands matching any of these regexes from being written to history.
## Note that these regular expressions are unanchored, i.e. if they don't start
## with ^ or end with $, they'll match anywhere in the command.
## For details on the supported regular expression syntax, see
## https://docs.rs/regex/latest/regex/#syntax
history_filter = [
   "^secret-cmd",
   "^innocuous-cmd .*--secret=.+"
]

Fixes #515

[conradludgate]

Thanks!

[ellie]

Very nice - thank you!