Allow persistent arguments

[gvol]

Since ripgrep doesn't support an rc file and doesn't plan to, it's very important to me that I can save some arguments (e.g. --smart-case and --type-add) that I always want to use.

In other words a defcustom that can be overwritten at run time, but usually won't be.

[kermorgant]

Same here, I was interested by adding a -M 200 argument to filter out long lines, which are so painful when they popup in the results

[BurntSushi]

Note that ripgrep does support config files now.