Create ABCheckPlus

This an updated version of an ABCheck function from the class. The original function asked to return true if the letter A or B could be found in a string separated by three spaces.

I have added to this function so that it is more robust. 
- You can specify two letters--not necessarily A or B. 
- You can specify a unique number of spaces-- not necessarily 3.
- The function also checks that the string is long enough.
Merge pull request #9 from DCeppos/Day3

Create ABCheckPlus