support reading RIPGREP_CONFIG_FILE

[acheronfail]

Fixes #98

To Do:

• [x] tests
• [x] handle the case of cli arguments overriding one another (i.e., --sort=path in config file, and --sort=modified on command line)
  • unsure about how to solve this nicely... clap's API isn't flexible enough for provide context about args, or to be able to merge arguments (as far as I know).
  • Investigate looking into clap's ArgMatches::ids method - we may be able to use that to merge
  • sorted out the above by re-writing our argument parsing, see below comments

[acheronfail]

Getting this right and in a maintainable way is actually rather difficult with what we have. Basically, the requirement is that rgr needs to do some parsing to get the information it needs, but also allow passing other options to rg.

These are the flags that rgr needs to know:

• all the flags relating to regex patterns:
  • pattern (positional argument)
  • -e or --regexp (mulitple allowed)
  • -f of --file (point to a file with regular expressions per line)
• -E or --encoding so we know how to handle file encodings
• -F or --fixed-strings so we know if we should be doing substring searches or regex searches

These are the flags that are unsupported by rgr:

• flags related to printing binary (since printing these can break the TUI):
  • --binary or -uuu
    • we can disable this with --no-binary
  • -a or --text
    • we can disable this with --no-text

Then, rgr itself will spawn rg with the --json flag, since we parse its JSON output to power its UI. The --json flag itself disallows some of rg's other options, but rg itself handles that so we don't have to. We can also disable the binary-related flags when spawning too, to override any if they were set.

Thus, the requirements for our argument parsing are to "sniff" our cmdline for the flags we need to know, bail out if we see a flag we don't support, and pass everything else through. We must also take into consideration the --config flag, since if it or RIPGREP_CONFIG_FILE is set, then we also need to sniff through the config file for any of the options we need.

I'm leaning towards re-writing rgr's argument parsing logic, since clap isn't exactly the right tool for this kind of thing, and it's only really being used as a whitelist anyway.

[acheronfail]

A fair amount of changes, especially some to CI, but they've been tested and things are looking good.

I'm going to create a release with the changes so far and see how it goes.