(squashed) added ABC Problem with contains_char
Merge pull request #168 from pfalabella/abc-problem

added ABC Problem
Renamed a+b.rs to a_plus_b.rs
(re-squashed) to_str() -> to_string() - now builds
Merge pull request #169 from pfalabella/to-str-remove

to_str() -> to_string()
(squashed) added Run-length encoding + comment
Merge pull request #171 from pfalabella/look-and-say

added Look-and-say sequence