Adding 'String search filter' functionality
Hey everyone,

I was working on a project that involves working with data acquired via the world bank pandas api (i.e. `pandas.io.wb`). This library has a function called `pandas.io.wb.search(str)` which is very useful. In data transformation terms, it's basically does this- given a string 's', filter the dataframe by retaining only the tuples where a string match occurs with the given string 's'.

This operation occurs in my workflow on a regular basis, and I was wondering if anyone else feels the need to have this function natively in pandas. Would be a huge time saver in my opinion!

Was thinking of a function that looks like this:
`DataFrame.search(search_str, is_ignore_case=True, is_match_full_word=False, **kwargs)`

Would love to hear from the community! :)
