Add checks for whether a string is in another string

[tjk]

Hey there!

I'll squash and rebase after some feedback.

1. could you please let me know if you are interested in this feature?
2. am I missing something when it comes to the current state of the .gitignore?
3. I put this patch together quickly and could have missed something obvious...
4. I'll be testing this shortly, but wanted to just get this up ASAP.
5. my vim config automatically changes some whitespace -- let me know if you want me to do undo those changes, please.
6. I just noticed in the other PR there are unit tests somewhere... didn't notice them in quick glance + should I update example directory?

Thanks for any comments!

[lpabon]

Hi @tjk , I'll make some time this week to review it. Thank you for the patch.

[lpabon]

@tjk Sorry, it has taken me so long to review this. I just finished my latest project Heketi. I'm reviewing now

[lpabon]

@tjk Just reviewed your code. I really, really like this. Please let me know if you have time to add unit tests since it has been a while.