Implementation for text_grep - Issue (Searcher (rustcore) #1715)

[itsmesamster]

[DmitryAstafyev]

@itsmesamster thanks for PR. I have a couple of comments in general:

• do not mix async and stuff from std. I'm about threads, channels etc from std... If you need to spawn something it should be really motivated and we should use tokio to do it (because it's major framework for chipmunk)
• try to keep away from Arc, Mutex etc... many use-cases can be resolved avoiding it.
• make sure you do not post any into terminal... It's crate/lib - it should return status. We can post something only for debugging
• please define Error enum for errors of your crate. Take a look to thiserror crate, which can be useful for string converting
• please add some information about measurements...

[itsmesamster]

Some random measurements and proof that the count is correct as per ripgrep, depending on the case sensitivity flag.