Add init support for a user defined PATH/glob cmd

[goodboy]

An attempt to resolve #112.

I'm not sure if this kinda thing will make all that much sense for AOT compiled langs (since often getting lib symbols isn't so straight forward as running some command to produce source-code-file-containing directories) but, it definitely is a thing in a language like python which users often dev / deploy in "isolated" runtime environments ("virtual envs"). In this case I have defined my custom glob scanner as:

let g:any_jump_glob_scanner = join([
    \'python',
    \'-c',
    \'"import os, site;',
    \"print(' '.join('{}'.format(d)",
    \'for d in site.getsitepackages()))',
    \'"',
    \])

which allows searching symbol defs in the user's locally activated python runtime env and thus the env specific ../site-packages/*.

---

Also included are some slight formatting tweaks in a couple of spots that seemed to have extra whitespace and a couple tweaks to the rg -g '!<globpatt>' quoting to work better when echoing the full cmd from vim for manuall copy/pasta debugging.

---

Still TODO

• [ ] the new global g:any_jump_glob_scanner and its value is only conditionally used inside RunRgDefinitionSearch() (for now, not sure if in side RunRgUsagesSearch() is also useful/warranted?) -[ ] currently only implemented thus far for rg backend
  • [ ] not sure if it's "smarter" to avoid use of rg -u filter removal and instead use -g <PATH> or some other >.gitignore override thingy?
• [ ] ag support!
  • [ ] wtv similar optimizations as done in rg

[goodboy]

Huh interestingly I seem to be getting some weird relative path thing when trying to "preview" the context of a given match?

it seems to be slapping the home-dir path in twice?