Anti join

[zander-prinsloo]

1. Add anti join to the joyn() function
2. Add dplyr-like anti_join()

Note, the update_values and update_NAs capabilities are removed because it does not make sense with an anti join.

All checks are passed.

[randrescastaneda]

HI @zander-prinsloo ,

I think the PR is correct. Thanks! Just a minor comment on one condition. Let me know if the comment is relevant. If not, please merge, and pump up the version to next devel version (the one with 9000+). You can do it using devtools::use_version() in case you did not know. Thank you!

[randrescastaneda]

Is this condition ok? I thought you had to remove "semi" rather than "anti"... Please disregard this comment is does not make sense.

[zander-prinsloo]

Hi @randrescastaneda , I believe what we are doing here works. However, even the condition of keep == "semi" is irrelevant because we do not yet allow semi joins for joyn::joyn(). I am going to remove this condition.

I did, however, add more tests for joyn() to test that the m:m anti join works since you identified this.