Add option to include children node (and corrections on readme.md)

[changhenry2]

I found this program because of ogrep by Matt Brubeck
and I found it giving more useful options than the "original" ogrep (eg. highlighting, listing line number).

1. Suggestion
   Is is possible to add an option (-c for children?) to list "children node" when printing out the results?
   Reason: I want use ogrep for searching information in plain text notes, children nodes offer more detailed information relating to the keywords (I personally believe that is how people take notes).
   I tried to revise the source code myself (changing the true/false in obsolete_context) but could not succeed.
   Could you consider adding this option, thanks!

2. Correction
   In readme.md, "otools" appears several times. I guess that was the original name of ogrep?
   for example,

otool in intended to search in single file only.

I believe it should be

ogrep is intended to search in single file only.

[Mikhail Trishchenkov]

I just added --children option to [ogrep-rs](Rust version of ogrep), you may have a look at it, it is faster and more featureful. I will eventually add this option to this ogrep too.

[changhenry2]

Thanks for your help!
I've submitted another issue related to search to ogrep-rs repository.